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Title: The Philosophy of Health; Volume 1 (of 2)

Author: Southwood Smith

Release date: November 23, 2019 [eBook #60773]

Language: English

Credits: Produced by Chris Curnow, Brian Wilsden and the Online
        Distributed Proofreading Team at http://www.pgdp.net (This
        file was produced from images generously made available
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*** START OF THE PROJECT GUTENBERG EBOOK THE PHILOSOPHY OF HEALTH; VOLUME 1 (OF 2) ***




Produced by Chris Curnow, Brian Wilsden and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive)





TRANSCRIBER'S NOTE: Italic text is denoted by _underscores_ and bold
text by =equal signs=.




  THE

  PHILOSOPHY OF HEALTH;

  OR,

  AN EXPOSITION

  OF THE

  PHYSICAL AND MENTAL CONSTITUTION
  OF MAN,

  WITH A VIEW TO THE PROMOTION OF

  HUMAN LONGEVITY AND HAPPINESS.

  BY

  SOUTHWOOD SMITH, M.D.,

  _Physician to the London Fever Hospital, to the Eastern Dispensary,
  and to the Jews' Hospital._

  IN TWO VOLUMES. VOL. I.

  _THIRD EDITION._

  LONDON:
  C. COX, 12, KING WILLIAM STREET, STRAND.

  1847.




London: Printed by W. CLOWES and SONS, Stamford Street.




CONTENTS OF VOL. I.


    INTRODUCTION                                                Page 1


    CHAPTER I.

    Characters by which living beings are distinguished
    from inorganic bodies—Characters by which
    animals are distinguished from plants—Actions
    common to plants and animals—Actions peculiar
    to animals—Actions included in the ORGANIC
    circle—Actions included in the ANIMAL
    circle—Organs and functions defined—Action of
    physical agents on organized structures—Processes
    of supply, and processes of waste—Reasons why the
    structure of the animal is more complex than that
    of the plant                                                    13


    CHAPTER II.

    Two distinct lives combined in the
    animal—Characters of the apparatus of the organic
    life—Characters of the apparatus of the animal
    life—Characteristic differences in the action of
    each—Progress of life—Progress of death                       51


    CHAPTER III.

    Ultimate object of organization and life—Sources
    of pleasure—Special provision by which the
    organic organs influence consciousness and afford
    pleasure—Point at which the organic organs cease
    to affect consciousness and why—The animal
    appetites: the senses: the intellectual faculties:
    the selfish and sympathetic affections: the moral
    faculty—Pleasure the direct, the ordinary,
    and the gratuitous result of the action of the
    organs—Pleasure conducive to the development
    of the organs, and to the continuance of their
    action—Progress of human knowledge—Progress of
    human happiness                                                 73


    CHAPTER IV.

    Relation between the physical condition
    and happiness, and between happiness and
    longevity—Longevity a good, and why—Epochs of
    life—The age of maturity the only one that admits
    of extension—Proof of this from physiology—Proof
    from statistics—Explanation of terms—Life a
    fluctuating quantity—Amount of it possessed in
    ancient Rome: in modern Europe: at present in
    England among the mass of the people and among the
    higher classes                                                 106


    CHAPTER V.

    Ultimate elements of which the body is composed—
    Proximate principles—Fluids and solids—Primary tissues—
    Combinations—Results—Organs, systems, apparatus—
    Form of the body—Division into head, trunk, and
    extremities—Structure and function of each—Regions—
    Seats of the more important internal organs                   148


    CHAPTER VI.

    Of the blood—Physical characters of the blood:
    colour, fluidity, specific gravity, temperature;
    quantity—Process of coagulation—Constituents of
    the blood; proportions —Constituents of the body
    contained in the blood—Vital properties of the
    blood—Practical applications                                  334


    CHAPTER VII.

    Of the circulation—Vessels connected with the
    heart; chambers of the heart—Position of the
    heart—Pulmonic circle; systemic circle—Structure
    of the heart, artery, and vein—Consequences
    of the discovery of the circulation to the
    discoverer—Action of the heart; sounds occasioned
    by its different movements—Contraction;
    dilatation—Disposition and action of the
    valves—Powers that move the blood—Force of
    the heart—Action of the arterial tubes; the
    pulse; action of the capillaries; action of the
    veins—Self-moving power of the blood—Vital
    endowment of the capillaries; functions—Practical
    applications                                                   357


    FOOTNOTES.                                                     408




INTRODUCTION.


The object of the present work is to give a brief and plain account
of the structure and functions of the body, chiefly with reference
to health and disease. This is intended to be introductory to an
account of the constitution of the mind, chiefly with reference to
the development and direction of its powers. There is a natural
connexion between these subjects, and an advantage in studying them
in their natural order. Structure must be known before function can
be understood: hence the science of physiology is based on that of
anatomy. The mind is dependent on the body: hence an acquaintance with
the physiology of the body should precede the study of the physiology
of the mind. The constitution of the mind must be understood before its
powers and affections can be properly developed and directed: hence a
knowledge of the physiology of the mind is essential to a sound view of
education and morals.

In the execution of the first part of this work, that which relates
to the organization of the body, a formidable difficulty presents
itself at the outset. The explanation of structure is easy when the
part described can be seen. The teacher of anatomy finds no difficulty
in communicating to the student a clear and exact knowledge of the
structure of an organ; because, by the aid of dissection, he resolves
the various complex substances, of which it is built up, into their
constituent parts, and demonstrates the relation of these elementary
parts to each other. But the case is different with him who attempts
to convey a knowledge of the structure of an organ merely by the
description of it. The best conceived and executed drawing is a
most inadequate substitute for the object itself. It is impossible
wholly to remove this difficulty: what can be done, by the aid of
plates, to lessen it, is here attempted. A time may come when the
objects themselves will be more generally accessible: meanwhile, the
description now given of the chief organs of the body may facilitate
the study of their structure to those who have an opportunity of
examining the organs themselves, and will, it is hoped, enable every
reader at once to understand much of their action.

Physical science has become the subject of popular attention, and
men of the highest endowments, who have devoted their lives to the
cultivation of this department of knowledge, conceive that they can
make no better use of the treasures they have accumulated, than that of
diffusing them. Of this part of the great field of knowledge, to make
"the rough places plain, and the crooked places straight," is deemed a
labour second in importance only to that of extending the boundaries of
the field itself. But no attempt has hitherto been made to exhibit a
clear and comprehensive view of the phenomena of life; the organization
upon which those phenomena depend; the physical agents essential
to their production, and the laws, as far as they have yet been
discovered, according to which those agents act. The consequence is,
that people in general, not excepting the educated class, are wholly
ignorant of the structure and action of the organs of their own bodies,
the circumstances which are conducive to their own health, the agents
which ordinarily produce disease, and the means by which the operation
of such agents may be avoided or counteracted; and they can hardly be
said to possess more information relative to the connexion between the
organization of the body and the qualities of the mind, the physical
condition and the mental state; the laws which regulate the production,
combination, and succession of the trains of pleasurable and painful
thought, and the rules deducible from those laws, having for their
object such a determination of voluntary human conduct, as may secure
the pleasurable and avoid the painful.

Yet nothing would seem a fitter study for man than the nature of man in
this sense of the term. A knowledge of the structure and functions of
the body is admitted to be indispensable to whoever undertakes, as the
business of his profession, to protect those organs from injury, and to
restore their action to a sound state when it has become disordered;
but surely some knowledge of this kind may be useful to those who
have no intention to practise physic, or to perform operations in
surgery; may be useful to every human being, to enable him to take a
rational care of his health, to make him observant of his own altered
sensations, as indications of approaching sickness; to give him the
power of communicating intelligibly with his medical adviser respecting
the seat and the succession of those signs of disordered function, and
to dispose and qualify him to co-operate with his physician in the use
of the means employed to avert impending danger, or to remove actual
disease.

But if to every human being occasions must continually occur, when
knowledge of this kind would be useful, the possession of it seems
peculiarly necessary to those who have the exclusive care of infancy,
almost the entire care of childhood, a great part of the care of
the sick, and whose ignorance, not the less mischievous because its
activity is induced by affection, constantly endangers, and often
defeats, the best concerted measures of the physician.

The bodily organization and the mental powers of the child depend
mainly on the management of the infant; and the intellectual and
moral aptitudes and qualities of the man have their origin in the
predominant states of sensation, at a period far earlier in the history
of the human being than is commonly imagined. The period of infancy is
divided by physiologists into two epochs; the first, commencing from
birth, extends to the seventh month: the second, commencing from the
seventh month, extends to the end of the second year, at which time
the period of infancy ceases, and that of childhood begins. The first
epoch of infancy is remarkable for the rapidity of the development
of the organs of the body: the processes of growth are in extreme
activity; the formative predominates over the sentient life, the chief
object of the action of the former being to prepare the apparatus
of the latter. The second epoch of infancy is remarkable for the
development of the perceptive powers. The physical organization of
the brain, which still advances with rapidity, is now capable of a
greater energy, and a wider range of function. Sensation becomes more
exact and varied; the intellectual faculties are in almost constant
operation; speech commences, the sign, and, to a certain extent, the
cause of the growing strength of the mental powers; the capacity of
voluntary locomotion is acquired, while passion, emotion, affection,
come into play with such constancy and energy, as to exert over the
whole economy of the now irritable and plastic creature a prodigious
influence for good or evil. If it be, indeed, possible to make correct
moral perception, feeling, and conduct, a part of human nature, as much
a part of it as any sensation or propensity—if this be possible for
every individual of the human race, without exception, to an extent
which would render _all_ more eminently and consistently virtuous than
_any_ are at present (and of the possibility of this, the conviction
is the strongest in the acutest minds which have studied this subject
the most profoundly), preparation for the accomplishment of this object
must be commenced at this epoch. But if preparation for this object
be really commenced, it implies, on the part of those who engage in
the undertaking, some degree of knowledge; knowledge of the physical
and mental constitution of the individual to be influenced; knowledge
of the mode, in which circumstances must be so modified in adaptation
to the nature of the individual being, as to produce upon it, with
uniformity and certainty, a given result. The theory of human society,
according to its present institutions, supposes that this knowledge is
possessed by the mother; and it supposes, further, that this adaptation
will actually take place in the domestic circle through her agency.
Hence the presumed advantage of having the eye of the mother always
upon the child; hence the apprehension of evil so general, I had almost
said instinctive, whenever it is proposed to take the infant, for the
purpose of systematic physical and mental discipline, from beyond the
sphere of maternal influence. But society, which thus presumes that
the mother will possess the power and the disposition to do this, what
expedients has it devised to endow her with the former, and to secure
the formation of the latter? I appeal to every woman whose eye may
rest on these pages. I ask of you, what has ever been done for you to
enable you to understand the physical and mental constitution of that
human nature, the care of which is imposed upon you? In what part of
the course of your education was instruction of this kind introduced?
Over how large a portion of your education did it extend? Who were
your teachers? What have you profited by their lessons? What progress
have you made in the acquisition of the requisite information? Were
you at this moment to undertake the guidance of a new-born infant to
health, knowledge, goodness, and happiness, how would you set about
the task? How would you regulate the influence of external agents upon
its delicate, tender, and highly-irritable organs, in such a manner
as to obtain from them healthful stimulation, and avoid destructive
excitement? What natural and moral objects would you select as the best
adapted to exercise and develope its opening faculties? What feelings
would you check, and what cherish? How would you excite aims; how would
you apply motives? How would you avail yourself of pleasure as a final
end, or as the means to some further end? And how would you deal with
the no less formidable instrument of pain? What is your own physical,
intellectual, and moral state, as specially fitting you for this
office? What is the measure of your own self-control, without a large
portion of which no human being ever yet exerted over the infant mind
any considerable influence for good? There is no philosopher, however
profound his knowledge, no instructor, however varied and extended his
experience, who would not enter upon this task with an apprehension
proportioned to his knowledge and experience; but knowledge which men
acquire only after years of study, habits which are generated in men
only as the result of long-continued discipline, are expected to come
to you spontaneously, to be born with you, to require on your part no
culture, and to need no sustaining influence.

But, indeed, it is a most inadequate expression of the fact, to say
that the communication of the knowledge, and the formation of the
habits which are necessary to the due performance of the duties of
women, constitute no essential part of their education: the direct
tendency of a great part of their education is to produce and foster
opinions, feelings, and tastes, which positively disqualify them for
the performance of their duties. All would be well if the marriage
ceremony, which transforms the girl into the wife, conferred upon the
wife the qualities which should be possessed by the mother. But it is
rare to find a person capable of the least difficult part of education,
namely, that of communicating instruction, even after diligent study,
with a direct view to teaching; yet an ordinary girl, brought up in
the ordinary mode, in the ordinary domestic circle, is intrusted with
the direction and control of the first impressions that are made upon
the human being, and the momentous, physical, intellectual, and moral
results that arise out of those impressions!

I am sensible of the total inadequacy of any remedy for this
evil, short of a modification of our domestic institutions. Mere
information, however complete the communication of it, can do little
beyond affording a clearer conception of the end in view, and of
the means fitted to secure it. Even this little, however, would be
something gained; and the hope of contributing, in some degree, to
the furtherance of this object, has supplied one of the main motives
for undertaking the present work. Meantime, women are the earliest
teachers; they must be nurses; they can be neither, without the risk
of doing incalculable mischief, unless they have some understanding
of the subjects about to be treated of. On these grounds I rest their
_obligation_ to study them; and I look upon that notion of delicacy,
which would exclude them from knowledge calculated, in an extraordinary
degree, to open, exalt, and purify their minds, and to fit them for the
performance of their duties, as alike degrading to those to whom it
affects to show respect, and debasing to the mind that entertains it.

Though each part of this work will be made as complete in itself as
the author is capable of rendering it, and to that extent independent
of any other part, yet there will be found to be a strict connexion
between the several portions of the whole; and greatly as the topics
included in the latter differ from those which form the earlier
subjects, the advantage of having studied the former before the latter
are entered on, will be felt precisely as the word _study_ can be
justly applied to the operation of the mind on such matters.

In the expository portion of the work I have not been anxious to
abstain from the employment of technical terms, when a decidedly useful
purpose was to be obtained by the introduction of them; but I have been
very careful to use no such term without assigning the exact meaning
of it. A technical term unexplained is a dark spot on the field of
knowledge; explained, it is a clear and steady light.

In order really to understand the states of health and disease,
an acquaintance with the nature of organization, and of the vital
processes of which it is the seat and the instrument, is indispensable:
it is for this reason that the exposition of structure and function,
attempted in this first part of the work, is somewhat full; but there
cannot be a question that, if it accomplish its object, it will not
only enable the account of health and disease in the subsequent part of
it to be much more brief, but that it will, at the same time, render
that account more intelligible, exact, and practical.

  S. S.




THE

PHILOSOPHY OF HEALTH.




CHAPTER I.

  Characters by which living beings are distinguished
  from inorganic bodies—Characters by which animals are
  distinguished from plants—Actions common to plants and
  animals—Actions peculiar to animals—Actions included in the
  organic circle—Actions included in the animal circle—Organs
  and functions defined—Action of physical agents on
  organized structures—Processes of supply, and processes
  of waste—Reasons why the structure of the animal is more
  complex than that of the plant.


The distinction between a living being and an inorganic body,
between a plant and a stone, is, that the plant carries on a number
of processes which are not performed by the stone. The plant absorbs
food, converts its food into its own proper substance, arranges this
substance into bark, wood, vessels, leaves, and other organized
structures; grows, arrives at maturity, and decays; generates and
maintains a certain degree of heat; derives from a parent the primary
structure and the first impulse upon which these varied actions depend;
gives origin to a new being similar to itself, and, after a certain
time, terminates its existence in death.

No such phenomena are exhibited by the stone; it neither absorbs
food, nor arranges the matter of which it is composed into organized
structure; nor grows, nor decays, nor generates heat, nor derives its
existence from a parent, nor gives origin to a new being, nor dies.
Nothing analogous to the processes by which these results are produced,
is observable in any body that is destitute of life; all of them are
carried on by every living creature. These processes are, therefore,
denominated vital, and, being peculiar to the state of life, they
afford characters by which the living being is distinguished from the
inorganic body.

In like manner the distinction between an animal and a plant is, that
the animal possesses properties of which the plant is destitute. It is
endowed with two new and superior powers, to which there is nothing
analogous in the plant; namely, the power of sensation, and the power
of voluntary motion; the capacity of feeling, and the capacity of
moving from place to place as its feeling prompts. The animal, like
the plant, receives food, transforms its food into its own proper
substance, builds this substance up into structure, generates, and
maintains a certain temperature, derives its existence from a parent,
produces an offspring like itself, and terminates its existence in
death. Up to this point the vital phenomena exhibited by both orders of
living creatures are alike: but at this point the vital processes of
the plant terminate, while those of the animal are extended and exalted
by the exercise of the distinct and superior endowments of sensation
and voluntary motion. To feel, and to move spontaneously, in accordance
with that feeling, are properties possessed by the animal, but not by
the plant; and therefore these properties afford characters by which
the animal is distinguished from the plant.

The two great classes of living beings perform, then, two distinct
sets of actions: the first set is common to all living creatures; the
second is peculiar to one class: the first set is indispensable to
life; the second is necessary only to one kind of life, namely, the
animal. The actions included in the first set, being common to all
living or organized creatures, are called ORGANIC; the actions included
in the second class, belonging only to one part of living or organized
creatures, namely, animals, are called ANIMAL. The ORGANIC actions
consist of the processes by which the existence of the living being is
maintained, and the perpetuation of its species secured: the ANIMAL
actions consist of the processes by which the living being is rendered
percipient, and capable of spontaneous motion. The ORGANIC processes
comprehend those of nutrition, respiration, circulation, secretion,
excretion, and reproduction; the first five relate to the maintenance
of the life of the individual being; the last to the perpetuation of
its species. The ANIMAL processes comprehend those of sensation and
of voluntary motion, often denominated processes of relation, because
they put the individual being in communication with the external
world. There is no vital action performed by any living creature
which may not be included in one or other of these processes, or in
some modification of some one of them. There is no action performed
by any inorganic body which possesses even a remote analogy to either
of these vital processes. The line of demarcation between the organic
and the inorganic world is, therefore, clear and broad; and the line
of demarcation between the two great divisions of the organic world,
between the inanimate and the animate, that is, between plants and
animals, is no less decided: for, of the two sets of actions which have
been enumerated, the one, as has just been stated, is common to the
whole class of living beings, while the second set is peculiar to one
division of that class. The plant performs only the organic actions:
all the vital phenomena it exhibits are included in this single circle;
it is, therefore, said to possess only organic life: but the animal
performs both organic and animal actions, and is therefore said to
possess both organic and animal life.

Both the organic and the animal actions are accomplished by means
of certain instruments, that is, organized bodies which possess a
definite structure, and which are moulded into a peculiar form. Such
an instrument is called an organ, and the action of an organ is called
its function. The leaf of the plant is an organ, and the conversion
of sap by the leaf into the proper juice of the plant, by the process
called respiration, is the function of this organ. The liver of the
animal is an organ; and the conversion of the blood that circulates
through it into bile, by the process of secretion, is its function. The
brain is an organ; the sentient nerve in communication with it is also
an organ. The extremity of the sentient nerve receives an impression
from an external object, and conveys it to the brain, where it becomes
a sensation. The transmission of the impression is the function of
the nerve; the conversion of the impression into a sensation is the
function of the brain.

The living body consists of a congeries of these instruments or
organs: the constituent matter of these organs is always partly in a
fluid and partly in a solid state. Of the fluids and solids which thus
invariably enter in combination into the composition of the organs, the
fluids may be regarded as the primary and essential elements, for they
are the source and the support of the solids. There is no solid which
is not formed out of a fluid; no solid which does not always contain,
as a constituent part of it, some fluid, and none which is capable of
maintaining its integrity without a continual supply of fluids.

Whatever be the intimate composition of the fluids out of which the
solids are formed, the investigation of which is more difficult than
that of the solids and the nature of which is therefore less clearly
ascertained, it is certain that all the matter which enters into
the composition of the solid is disposed in a definite order. It is
this disposition of the constituent matter of the living solid in a
definite order that constitutes the arrangement so characteristic of
all living substance. Definite arrangements are combined in definite
modes, and the result is what is termed organization. From varied
arrangements result different kinds of organized substances, each
endowed with different properties, and exhibiting peculiar characters.
By the recombination of these several kinds of organized substances,
in different proportions and different modes, are formed the special
instruments, or organs, of which we have just spoken; while it is the
combining, or the building up of these different organized substances
into organs, that constitutes structure.

In the living body, not only is each distinct organ alive, but, with
exceptions so slight that they need not be noticed here, every solid
which enters into the composition of the organ is endowed with vital
properties. This is probably the case with the primary substances or
tissues which compose the several organs of the plant; but that the
animal solids are alive is indubitable; nay, the evidence is complete,
that many even of the animal fluids possess vitality. The blood in the
animal is as truly alive as the brain, and the bone as the flesh. The
organized body, considered as a whole, is the seat of life; but life
also resides in almost every component part of it.

Yet the matter out of which these living substances is formed is not
alive. By processes of which we know nothing, or, at least, of which
we see only the first steps,—matter, wholly destitute of life, is
converted into living substance. The inorganic matter, which is the
subject of this wonderful transformation, is resolvable into a very
few elementary substances. In the plant, these substances consist of
three only, namely, oxygen, hydrogen, and carbon. The first two are
aëriform or gaseous bodies; the last is a solid substance, and it is of
this that the plant is chiefly composed: hence the basis of the plant
is a solid. The elementary bodies, into which all animal substance is
resolvable, are four, namely, azote, oxygen, hydrogen, and carbon.
Into every animal fluid and solid this new substance azote enters so
largely, that it may be considered as the fundamental and distinctive
element of the animal organization: hence the basis of the animal is
an aëriform or gaseous fluid. The animal is composed of air, the plant
of solid matter; and this difference in their elementary nature gives
origin to several distinctive characters between the plant and the
animal, in addition to those which have been already stated.

Thus the characters of the plant are solidity, hardness, fixedness, and
durability; while the animal is comparatively fluid, soft, volatile,
and perishable; and the reason is now manifest. The basis of the animal
being an aëriform fluid, its consistence is softer than that of the
plant, the basis of which is a firm solid; and, at the same time, the
component elements of the animal being more numerous than those of the
plant, and the fluidity of these elements, and of the compounds they
form, greatly favouring their action and reaction on each other and on
external agents, the animal body is more volatile and perishable during
life, and more readily decomposed after death.

It has been stated, that the object of every structure or organ
of the living body, is the performance of some special action or
function,—the ultimate object of the fluids being the production of
the solids; the ultimate object of the solids being the formation of
organs; the ultimate object of organs being the performance of actions
or functions; while it is in the performance of actions or functions
that life consists. Functions carried on by organs; organs in action;
special organs performing definite actions, this it is that constitutes
the state of life. Every particle of matter which enters into the
composition of the living body has thus its own place, forming, or
destined to form, a constituent part of some organ; every organ has
its own action; all the organs of the body form the body; and all
the actions of all the organs constitute the aggregate of the vital
phenomena.

Every organ is excited to action, or its function is called into
operation by means of some external body. The external bodies capable
of exciting and maintaining the functions of living organs, consist
of a definite class. Because these bodies belong to that department
of science which is called physical, they are termed physical agents.
They are air, water, heat, cold, electricity, and light. Without the
living organ, the physical agent can excite no vital action: without
the physical agent, the living organ can carry on no vital process.
The plant cannot perform the vital process of respiration without the
leaf, nor, with the leaf, without air. The physical agent acts upon the
living organ; the living organ reacts upon the physical agent, and the
action between both is definite. In the lung of the animal a certain
principle of the air unites, in definite proportions, with a certain
principle of the blood; the oxygen of the air combines with the carbon
of the blood; the air is changed by the abstraction of its oxygen;
the blood is changed by the abstraction of its carbon. Atmospheric
air goes to the lung, but atmospheric air does not return from the
lung; it is converted into a new substance by the action of the organ:
it is changed into carbonic acid by the union of a given quantity of
oxygen, which it transmits to the organ, with a given quantity of
carbon which the organ conveys to it. Venous blood goes to the lung,
but venous blood does not return from the lung; it is converted, by
the instrumentality of the organ, into a new substance, into arterial
blood, by giving to the air carbon, and by receiving from the air
oxygen. In this manner the change in the physical agent is definite and
uniform; and the change in the living substance is equally definite and
uniform.

It is this determinate interchange of action between the living organ
and the physical agent that constitutes what is termed a vital process.
All vital processes are carried on by living organs; the materials
employed in all vital processes are physical agents; the processes
themselves are vital functions. All the changes produced by all the
organs of the plant upon physical agents, and all the changes produced
by all physical agents upon the organs of the plant, constitute all
the vital processes of the plant—comprehend the whole sum of its
vital phenomena. The root, the trunk, the woody substance, the bark,
the ascending vessels bearing sap, the descending vessels bearing
secreted fluids, the leaves, the flowers, these are the living organs
of the plant. Air, water, heat, cold, electricity, light, these are the
physical agents which produce in these organs definite changes, and
which are themselves changed by them in definite modes; and the whole
of these changes, taken together, comprehend the circle of actions, or
the range of functions performed by this living being.

In the state of life, during the interchange of action which thus
incessantly goes on between physical agents and vital organs, the
laws to which inorganic matter is subject are resisted, controlled,
and modified. Physical and chemical attractions are brought under the
influence of a new and superior agency, with the laws of which we are
imperfectly acquainted, but the operation of which we see, and which we
call the agency of life. Air, water, heat, electricity, are physical
agents, which subvert the most intimate combinations of inorganic
bodies, resolving them into their simple elements, and recombining
these elements in various modes, and thus forming new bodies, endowed
with totally different properties; but the physical and chemical
agencies by which these changes are wrought in the inorganic, are
resisted, controlled, and modified by the living body: resisted, for
these physical agents do not decompose the living body; controlled
and modified, for the living body converts these very agents into the
material for sustaining its own existence Of all the phenomena included
in that circle of actions which we designate by the general term life,
this power of resisting the effects universally produced by physical
agents on inorganic matter, and of bringing these very agents under
subjection to a new order of laws, is one of the most essential and
distinctive.

All vital processes are processes of supply, or processes of waste. By
every vital action performed by the organized body, some portion of its
constituent matter is expended. Numerous vital actions are constantly
carried on for the sole purpose of compensating this expenditure. Every
moment old particles are carried out of the system; every moment new
particles are introduced into it. The matter of which the organized,
and more especially the animal, body is composed, is thus in a state
of perpetual flux; and in a certain space of time it is completely
changed, so that of all the matter that constitutes the animal body at
a given point of time, not a single particle remains at another point
of time at a given distance.

All the wants of the economy of the plant are satisfied by a due
supply of air, water, heat, cold, electricity, and light. Some of
these physical agents constitute the crude aliment of the plant;
others produce in this aliment a series of changes, by which it is
converted from crude aliment into proper nutriment, while others act
as stimulants, by which movements are excited, the ultimate object of
which is the distribution of the nutriment to the various parts of the
economy of the plant.

The same physical agents are indispensable to the support of the animal
body; but the animal cannot be sustained by these physical agents
alone; for the maintenance of animal life, in some shape or other,
vegetable or animal matter, or both in a certain state of combination,
must be superadded: hence another distinction between the plant and the
animal,—the necessity, on the part of the animal, of an elaborated
aliment to maintain its existence. By the vital processes of its
economy, the plant converts inorganic into organic matter; by the vital
processes of its economy, the animal converts matter, already rendered
organic, into its own proper substance. The plant is thus purveyor to
the animal: but it is more than purveyor to it; for while it provides,
it also prepares its food; it saves the animal one process, that of
the transmutation of inorganic into organic matter. The ultimate end,
or the final cause of the vital processes performed by the first class
of living beings, is thus the elaboration of aliment for the second:
the inferior life is spent in ministering, and the great object of its
being is to minister to the existence of the superior.

At the point at which organization commences structure is so simple
that there is no manifest distinction of organs. Several functions are
performed apparently by one single organized substance. The lowest
plants and the lowest animals are equally without any separate organs,
as far as it is in our power to distinguish them, for carrying on the
vital actions they perform. An organized tissue, apparently of an
homogeneous nature, containing fluid matter, is all that can be made
out by which the most simply-constructed plant carries on its single
set, and by which the most simply-constructed animal carries on its
double set, of actions. But this simplicity of structure exists only
at the very commencement of the organized world. Every advancement in
the scale of organization is indicated by the construction of organs
manifestly separate for the performance of individual functions;
and, invariably, the higher the being, the more complete is this
separation of function from function, and, consequently, the greater
the multiplication of organs, and the more elaborate and complex the
structure;—and hence another distinction between the plant and the
animal. The simplicity of the structure of the plant is in striking
contrast to the complexity of the structure of the animal; and this
difference is not arbitrary; it is a matter of absolute necessity, and
the reason of this necessity it will be instructive to contemplate.

The plant, as has been shown, performs only one set of functions, the
organic; while the animal performs two sets of functions, the organic
and the animal. The animal, then, performs more functions than the
plant, and functions of a higher order; it carries on its functions
with a greater degree of energy; its functions have a more extended
range, and all its functions bear a certain relation to each other,
maintaining an harmonious action. The number, the superiority, the
relation, the range, and the energy of the functions performed by
the animal are, then, so many conditions, which render it absolutely
indispensable that it should possess a greater complexity of structure
than the plant.

1. To build up structure is to create, to arrange, and to connect
organs. Organs are the instruments by which functions are performed,
and without the instrument there can be no action. With as many
more organs than the plant possesses the animal must, therefore, be
provided, as are necessary to carry on the additional functions it
performs. Organs, for its organic functions, it must have as well as
the plant; but to these must be superadded organs of another class, for
which the plant has no need, namely, organs for its animal functions.
Two sets of organs must, therefore, be provided for the animal, while
the plant requires but one.

2. Some functions performed by the animal are of a higher order than
any performed by the plant, and the superior function requires a higher
organization. The construction of an organ is complex as its action is
elevated; the instrument is elaborately prepared in proportion to the
nobleness of its office.

[Illustration: Fig. I.]

[Illustration: Fig. II.]

[Illustration: Fig. III.]

[Illustration: Fig. IV.]

3. But this is not all; for the addition of a superior function
requires not only the addition of an organ having a corresponding
superiority of structure, but it requires, further, that a certain
elevation of structure should be communicated to all the organs of
all the inferior functions, on account of the relation which it is
necessary to establish between function and function. Unless the organ
of an inferior function be constructed with a perfection corresponding
to that of the organ of a superior function, the inferior will be
incapable of working in harmony with the superior. Take, for example,
the inferior function of nutrition: nutrition is an organic function
equally necessary to the plant and to the animal, and requiring in
both organs for performing it; but this function cannot be performed
in the animal by organs as simple as suffice for the plant. Nutrition,
in the plant, is carried on in the following mode:—The root of the
plant is divided, like the trunk, into numerous branches (fig. I. 1).
These branches divide and subdivide into smaller and smaller branches,
until at last they reach an extreme degree of minuteness (fig. I. 2 2).
The smallest of these divisions, called, from their hair-like tenuity,
_capillary_ (fig. I. 2 2), are provided with a peculiar structure,
which is endowed with a specific function. In most plants this peculiar
structure is found at the terminal point of the rootlet (fig. I. 2 2);
but in some plants the capillary branches of the rootlets are provided
with distinct bodies (fig. II. 1 2), scarcely to be discerned when
the root has been removed some time from the soil, and has become dry
(fig. II. 2 2); but which, in a few minutes after the root has been
plunged in water, provided the plant be still alive, become turgid with
fluid, and, consequently, distinctly visible (fig. II. 1 1 1). These
bodies, when they exist, or the terminal point of the rootlet when
these bodies are absent, are termed _spongeolæ_, or spongeoles; and the
structure and function of the organ, in both cases, are conceived to
be precisely the same. In both the organ consists of a minute cellular
structure. Fig. III. 1, shows this structure as it appears when the
object is magnified. The office of this organ is to absorb the aliment
of the plant from the soil; and so great is its absorbing power, that,
as is proved by direct experiment, it absorbs the colouring molecules
of liquids, though these molecules will not enter the ordinary pores,
which are of much greater magnitude. With the spongeoles are connected
vessels which pass through the substance of the stem or trunk to the
leaf. Fig. III. 2, shows these tubes springing from the cellular
structure of the spongeole, and passing up to the stem or trunk. Fig.
IV. 2, exhibits a magnified view of the appearance of the mouths of
these tubes on making an horizontal section of the spongeole. Fig. V.
1 1 1, exhibits a view of these tubes passing to the leaf. Figs. VI.
and VII. 1 1 1 1, show these vessels spread out upon, and ramifying
through, the leaf. The crude aliment, borne by these tubes to the leaf,
is there converted into proper nutriment; and from the leaf, when
duly elaborated, this proper nutriment is carried out by ducts to the
various organs of the plant, in order to supply them with the aliment
they need.

[Illustration: Fig. V.]

Now, for carrying on the process of nutrition in this mode, there
must be organs to absorb the crude aliment, organs to convey the crude
aliment to the laboratory, the leaf, in which it is converted into
proper nutriment; and, finally, organs for carrying out this proper
nutriment to the system. Complication of structure, to this extent, is
indispensable; and, accordingly, with spongeolæ, with sap-vessels, with
leaves, with distributive ducts, the plant is provided. Without all the
parts of this apparatus it could not carry on its function: any further
complication would be useless.

[Illustration: Fig. VI.]

But, suppose a new and superior function to be added to the plant;
suppose it to be endowed with the power of locomotion, what would be
the consequence of communicating to it this higher power? That its
former state of simplicity would no longer suffice for the inferior
function. Why? because the exercise of the superior would interrupt
the action of the inferior function. Nutrition by imbibition, and
the exercise of locomotion, cannot go on simultaneously in the same
being. The plant is fixed in the soil by its roots; and from this, its
state of immobility, results this most important consequence, that its
spongeolæ are always in contact with its food.

[Illustration: Fig. VII.]

[Illustration: Fig. VIII.]

But we may imagine a plant not fixed to the soil; a plant so
constituted as to be capable of moving from place to place; such a
plant would not be always in contact with its food, and therefore, as
it exercised its faculty of locomotion, it could not but interrupt
or suspend its function of nutrition. In a being capable of carrying
on these two functions simultaneously, the entire apparatus of the
function of nutrition must then be modified. Instead of having
spongeolæ fixed immovably in the earth, and spread out in a soil
adapted to transmit to these organs nutrient matter in a state fitted
for absorption, it must be provided with a reservoir for containing
its food, in order that it may carry its aliment about with it in
all its changes of place. And such is the modification uniformly
found in all animals: an internal reservoir for containing its food
is provided, perhaps, for every animal without exception. Even the
simplest and minutest creatures with which the microscope has made
us acquainted, the lowest tribes of the Infusoria (fig. VIII.), the
sentient, self-moving cellules, placed at the very bottom of the
animal scale, possess this modification of structure. For a long
time it was conceived that these minute and simple creatures were
without distinction of parts, that they had no separate organs for the
reception and digestion of their food; that they absorbed their aliment
through the porous tissue of which their body is composed; that thus,
instead of having a separate stomach, their entire body is a stomach,
and instead of having even as much as a separate organ for absorption,
like the more perfect plant, the whole body might be considered as a
single spongeole.

But, by a simple and beautiful experiment, a German physiologist
has shown the incorrectness of this opinion, and has established the
fact, that the distinction between the plant and the animal, here
contended for, is found even at the very lowest point of the animal
scale. Like other physiologists, conceiving that the difficulty of
discovering the structure of the lower tribes of the animalculi
might be owing to the transparency or the tissues of which they are
composed, it struck Ehrenberg, that if he could feed them with coloured
substances, he might obtain some insight into their organization.
In his first endeavours to accomplish this object he failed, for he
employed the pigments in ordinary use; but either the animals would not
touch aliment thus adulterated, or those that did so were instantly
killed. It then occurred to him, that these colours are adulterated
with lead and other substances, in all probability noxious to the
little subjects of his experiment. "What I require," said he, "is some
vegetable or animal colouring matter perfectly pure." He then tried
perfectly pure indigo and perfectly pure carmine. His success was
now complete: in a minute or two, after mixing with their food pure
vegetable colouring matter, he observed in the interior of the body of
these creatures minute spots of a definite figure, and of the colour
of the pigment employed (fig. VIII. 1 1 1 1). The form and magnitude
of these spots were different in different tribes, but the same in the
same individual, and even in the same species (fig. IX. 1 1, fig. X.
1 1). No other parts of the body were tinged with the colour, though
the animals remained in the coloured fluid for days together. This was
decisive. This physiologist had now obtained an instrument capable of
revealing to him the interior organization of a class of beings, the
structure of which had heretofore been wholly unknown. On applying
it to the MONAS TERMO (fig. VIII.), the animated point, or cellule,
which stands at the bottom of the animal scale, he discovered, in the
posterior portion of its body, several coloured spots which constitute
its stomachs (fig. VIII. 1 1 1 1). The different situations and
different forms of the stomach in different tribes of these creatures,
are represented by the coloured portions (fig. VIII. 1, fig. IX. 1,
fig. X. 1), in which the currents of fluid flowing to their mouths
are seen (fig. IX. 2, fig. X. 2). These experiments go far towards
establishing the fact, that every animal, even the very lowest, has an
external mouth and an internal stomach, and that it takes its food by
an act of volition.

[Illustration: Fig. IX.]

[Illustration: Fig. X.]

But if the proof of this must be admitted to be still imperfect
with regard to the lowest tribes of animals, it is certain that, as
we ascend in the scale of organization, the nutritive apparatus is
uniformly arranged in this mode. Every animal of every class large
enough to be distinctly visible, and the structure of which is not
rendered inappreciable by the transparency of its solids and fluids, is
manifestly provided with a distinct internal reservoir for containing
its food. On the internal surface of this reservoir open the mouths of
vessels, minute in size but countless in number, which absorb the food
from the stomach.

Fig. XI. shows these vessels opening on the inner surface of the
stomach, the white points representing their mouths, turgid with the
food they have absorbed. Fig. XII. exhibits magnified views of the same
vessels, the points representing their open mouths, and the lines the
vessels themselves in continuation with their mouths. Fig. XIII. shows
the appearance of the inner surface of the intestine soon after the
animal has taken food; the smaller white lines (1 1 1 1) representing
the absorbent vessels full of digested food, and the larger lines (2 2
2 2) the trunks of the absorbent vessels formed by the union of many of
the smaller.

[Illustration: Fig. XI.]

[Illustration: Fig. XII.]

From this account, it is clear that the absorbing vessels of the
stomach perform an office precisely analogous to that of the spongeoles
of the root. What the soil is to the plant, the stomach is to the
animal. The absorbing vessels diffused through the stomach, as long
as the stomach contains food, are in exactly the same condition as
the spongeoles of the root spread out in the soil; and the absorbing
vessels of the stomach are as much and as constantly in contact with
the aliment, which it is their office to take into the system, as the
spongeoles of the root. Such, then, is the expedient adopted to render
the function of nutrition compatible with the function of locomotion.
A reservoir of food is placed in the interior of the animal, provided
with absorbent vessels which are always in contact with the aliment. In
this mode, contact with aliment is not disturbed by continual change of
place; the organic process is not interrupted by the exercise of the
animal function.

[Illustration: Fig. XIII.]

But the more elaborate organization which it is necessary to impart
to the apparatus of the inferior function, in consequence of the
communication of a superior faculty, is not completed simply by the
addition of this new organ, the stomach. Other complications are
indispensable; for if food be contained in an isolated organ, placed in
the interior of the body, means must be provided for conveying the food
into this organ; hence the necessity of an apparatus for deglutition.
Moreover, the food having been conveyed to the stomach, and having
undergone there the requisite changes, means must next be provided for
conveying it from the stomach to the other parts of the body; hence
the necessity of an apparatus for the circulation. But food, however
elaborately prepared by the stomach, is incapable of nourishing the
body, until it has been submitted to the action of atmospheric air;
hence the necessity of an additional apparatus, either for conveying
food to the air, or for transmitting air to the food, or for bringing
both the food and the air into contact in the same organ. And, when
structure after structure has been built up, in order to carry on this
extended series of processes, the number of provisions required is
not even yet complete; for of the most nutritious fond the whole mass
is not nutritive; and even the whole of that portion of it which is
actually applied to the purpose of nutrition, becomes, after a time,
worn out, and must be removed from the system; hence the necessity of a
further apparatus for excretion.

That nutrition and locomotion may go on together, it is clear, then,
that there must be provided a distinct apparatus for containing
food, a distinct apparatus for deglutition, a distinct apparatus for
circulation, a distinct apparatus for respiration, a distinct apparatus
for excretion, and so on; and that, in this manner, the communication
of a single function of a superior order renders a modification not
merely of one but of many inferior functions absolutely indispensable,
in order to adjust the one to the other, and to enable them to act in
harmony.

But the necessary complication of structure does not stop even here;
for the communication of one function of a superior order imposes
the necessity of communicating still another. Locomotion cannot be
exercised without perception; sensation is indispensable to volition,
and volition, of course, to voluntary motion. A being endowed with
the power of moving from place to place, without possessing the power
of perceiving external objects, must be speedily destroyed. The
communication of sensation to a creature fixed immovably to a single
spot, conscious of the approach of bodies, but incapable of avoiding
their contact, would be not only useless but pernicious, since it
would be to make a costly provision for the production of pain, and
nothing else; but the communication of locomotion without sensation
would be as unwisely defective, as the former would be perniciously
expensive; since it would be to endow a being with a faculty, the
exercise of which would be fatal to it for the want of a second faculty
to guide the first. Nor could the possession of locomotion, without the
further possession of sensation, be otherwise than fatal, for another
reason. Consciousness is not necessary to nutrition as performed by
the plant, but it is indispensable to nutrition as performed by the
animal: for if the food of the animal be not always on the same spot
with itself; if it be under the necessity of searching for it, and of
conveying it, when found, into the interior of its body, it must, of
course, possess the power of perceiving it when within its reach, and
of apprehending and appropriating it by an act of volition, of none of
which actions is it capable without the possession of sensation. Again,
then, we see that, in order to secure harmonious action, function must
be put in relation with function. In order to prevent jarring and
mutually-destructive action, function must be superadded to function,
and throughout the animal creation the complication of structure, which
is necessary for the accomplishment of these ends, is given without
parsimony, but without profusion: nothing is given which is not needed,
nothing is withheld which is required.

4. As we ascend in the scale of organization, numerous functions being
carried on, and numerous organs constructed for performing them, it
is obvious that the range of each function must be proportionally
extended; the range necessarily increasing with the multiplication
of organ and function: and this is another cause of the unavoidable
complication of structure. Slight consideration will suffice to show
the necessary connexion between an extended range of action and
complication of structure. Take, as an example, the organic function
of respiration: respiration is the function by which air is brought
into contact with food; it is the completion of digestion. The sole
end of all the apparatus that belongs to this function is to bring the
air and the food into a certain degree of proximity. Now, when all the
substances that enter into the composition of the body of an animal are
slight, delicate, and permeable to air (as in fig. XIV.), and when the
body is always surrounded by air, air must at all times be in contact
with the particular organ that contains the food, no less than with
the general system to which the food is distributed. In this case, to
construct a separate apparatus for containing air would be useless,
because wherever food is, there air must be, since it constantly
permeates every part of the body.

[Illustration: Fig. XIV.]

When, on the other hand, the tissues are so firm and dense as to be
impermeable; when they are folded into bulky and complex organs, and
when these organs are placed in situations to which the external air
cannot reach, the construction of a separate apparatus for respiration
is indispensable. The respiratory apparatus consists either of organs
for carrying air to the food, or of organs for carrying food to the
air. The one or the other is adopted, according to the nature of the
body. If the size of the animal be small; if the tissues which form
the solid portion of its body be delicate in texture; if, at the same
time, the wants of its economy require that its food should be highly
aërated (for there is the closest connexion between energy of function
and perfect aëration of the food), an apparatus of sufficient magnitude
to aërate the food in a high degree would occupy the entire bulk of the
body. In such a case, it is easier to carry air to the food than food
to the air; it is better to make the entire body a respiratory organ,
than to construct a respiratory organ disproportioned to the magnitude
of the body. Air-tubes diffused through every part of the body, and
opening on its external surface, would obviously afford to every point
of the system an easy access of air. By an expedient of this kind the
system might be highly aërated, while the respiratory apparatus would
occupy but a comparatively small space; the function might be performed
on an extended scale, while there would be no necessity for encumbering
a minute body with a bulky organ. And this is the mode in which
respiration is carried on in large tribes of creatures, whose body
is small in size and delicate in texture, and the functions of whose
economy are performed with energy (fig. XV.).

[Illustration: Fig. XV.

  The Achilles Butterfly of South America (_Papilio Achilles_),
  showing the tracheæ on the upper and under side of the wings.]

But this contrivance will not do when the animal is of large
magnitude; when its body is divided into numerous compartments; when
these compartments extend far beneath the external surface; when
important organs are placed in deeply-seated cavities; and when
the substances that compose the organs are dense, hard, thick, and
convoluted. To construct air-tubes of the requisite diameter and
length, always open, always in a condition to permit the ingress and
egress of an adequate current of air to and from the remotest nook and
corner of a body such as this, would be difficult, if not impossible.
At all events, it is easier, in such a case, to carry the food to the
air, than the air to the food. But, for the accomplishment of this
purpose, what is necessary? An organ for containing food; an organ
for containing air; vessels to carry food to and from the receptacle
of the aliment; vessels to carry air to and from the receptacle of
the air; expedients to expose a stream of food to a current of air;
and, finally, tubes to carry out to the system the product of this
complicated operation. Accordingly, a reservoir of food and a reservoir
of air; an apparatus by which both are conveyed to their respective
receptacles; and an apparatus by which both are brought into contact
sufficiently close to admit of their mutual action, are all combined
in the lung of the animal, and in the mechanism by which its movements
are effected. The object is accomplished, but the apparatus by which it
is effected is as complex in structure as it is efficient in action;
the result simple; the means by which the result is secured, highly
complicated.

And if this be true of an inferior or organic function, it is still
more strikingly true of a superior or animal function. The relation is
still stricter between the complexity of the apparatus of sensation and
the range of feeling, than between the complexity of the apparatus of
respiration and the range of the respiratory process. The greater the
number of the senses, the greater the number of the organs of sense;
the more accurate and varied the impressions conveyed by each, the more
complex the structure of the instrument by which they are communicated;
the more extended the range of the intellectual operations, the larger
the bulk of the brain, the greater the number of its distinct parts,
and the more exquisite their organization. From the point of the animal
scale, at which the brain first becomes distinctly visible, up to man,
the basis of the organ is the same; but, as the range of its function
extends, part after part is superadded, and the structure of each part
becomes progressively more and more complex. The evidence of this,
afforded by comparative anatomy, is irresistible, and the interest
connected with the study of it can scarcely be exceeded.

5. In the last place, structure is complex in proportion to the
energy of function. The greater the power with which voluntary motion
is capable of being exerted, the higher the organization of the
apparatus by which it is performed; the more compact and dense the
shell, the cartilage, the bone, the firmer the fibre of the muscle,
and, in general, the greater its comparative bulk. The wing of the
eagle is as much more developed than the wing of the wren, as its
flight is higher, and its speed swifter. The muscles which give to the
tiger the rapidity and strength of its spring possess a more intense
organization than those which slowly move on the tardigrade sloth. The
structure of the brain of man is more exquisite than that of the fish,
as his perceptions are more acute, and capable of greater combination,
comprehension, and continuity.

Thus we see that the organization of the animal is more complex than
that of the plant, not from an arbitrary disposition, but from absolute
necessity. The few and simple functions performed by the plant require
only the few and simple organs with which it is provided: the numerous
and complicated functions performed by the animal require its numerous
and complicated organs: the plant, simple as it is in structure, is
destitute of no organ required by the nature of its economy; the
animal, complex as it is in structure, is in possession of no organ
which it could dispense with: from the one, nothing is withheld which
is needed; to the other, nothing is given which is superfluous: in the
one, there is economy without niggardliness; in the other, munificence
without waste.




CHAPTER II.

  Two distinct lives combined in the animal—Characters of the
  apparatus of the organic life—Characters of the apparatus of
  the animal life—Characteristic differences in the action of
  each—Progress of life—Progress of death.


Of the two sets of functions carried on by living beings, it has been
shown, that the plant performs only one, while the animal exercises
both. The two lives thus in continual play in the animal differ from
each other as much as the process of vegetation differs from that of
thought, yet they are united so closely, and act so harmoniously,
that their existence as distinct states is not only not apparent to
ordinary observation, but the very discovery of the fact is of recent
date, and forms one among the splendid triumphs of modern physiology.
Their action is perfect, yet their separate identity is so distinctly
preserved, that each has its own apparatus and its own action, which
are not only not the same, but, in many interesting circumstances, are
in striking contrast to each other.

1. In general the organs that belong to the apparatus of the organic
life are single, and not symmetrical; the organs that belong to the
apparatus of the animal life are either double, or symmetrical, or
both. As will be shown hereafter, the heart, the lungs, the stomach,
the intestines, the liver, the pancreas, the spleen, the instruments
by which the most important functions of the organic life are carried
on, are single organs. (Chap. 5.) The figure of each is more or less
irregular, so that if a line were carried through their centre, it
would not divide them into two equal and precisely corresponding
portions. On the contrary, the organs of the animal life are
symmetrical. The brain and the spinal cord are divisible into two
perfectly equal parts. (Chap. 5.) The nerves which go off from these
organs for the most part go off in pairs equal in size and similar
in distribution. (Ibid.) The trunk, so important an instrument of
voluntary motion, when well formed, is divisible into two perfectly
corresponding portions. (Ibid.) The muscular apparatus of one half
of the body is the exact counterpart of that of the other; while the
arms, the hands, and the lower extremities are not only double, but the
organization of the one is precisely similar to that of its fellow.

2. In general, the apparatus of the organic life is placed in the
interior of the body, while that of the animal life is placed on the
external surface. The organic organs are the instruments by which
life is maintained. There is no action of any one of them that can
be suspended even for a short space of time without the inevitable
extinction of life. But the animal organs are not so much instruments
of life as means by which a certain relation is established between the
living being and external objects. And this difference in their office
is the reason of the difference in their position. Existence depending
on the action of the organic organs, they are placed in the interior of
the body; they are fixed firmly in their situation in order that they
may not be disturbed by the movements of locomotion; they are enveloped
in membranes, covered by muscles, placed under the shelter of bones,
and every possible care is taken to secure them from accident and to
shield them from violence. Existence not being immediately dependent
on the action of the organs of the animal life, they do not need to
be protected from the contact of external objects with extraordinary
care, but it is necessary to the performance of their functions that
they should be placed at the exterior of the body. And there they are
placed, and so placed as to afford an effectual defence to the organic
organs. Thus the groundwork of the animal is made the bulwark of the
organic life. The muscles, the immediate agents by which voluntary
motion is effected, and the bones, the fixed points and the levers by
which that motion acquires the nicest precision and the most prodigious
rapidity and power, are so disposed that, while the latter accomplish,
in the most perfect manner, their primary and essential office in
relation to the muscles, they serve a secondary but scarcely less
important office in relation to the internal viscera. As we advance
in our subject, we shall see that a beautiful illustration of this is
afforded in the structure and action of the trunk; that the trunk is
moveable; that it is composed of powerful muscles, and of firm and
compact bones; and that while its movements are effected by the action
of the muscles which are attached to the bones, these bones enclose
a cavity, in which are placed the lungs, the heart, the great trunks
of the venous system, the great trunks of the arterial system, and
the main trunk of the thoracic duct, the vessel by which the digested
aliment is carried into the blood. (Chap. 5.) Thus, by these strong and
firm bones, together with the thick and powerful muscles that rest upon
them, is formed a secure shelter for a main portion of the apparatus
of the organic functions of respiration, circulation, and digestion.
The bones and muscles of the thorax, themselves performing an important
part in the function of respiration, afford to the lungs the chief
organ of this function, composed of tender and delicate tissues, easily
injured, and the slightest injury perilling life, a free and secure
place to act in. The fragile part of the apparatus is defended by the
osseous portion of it, the play of the latter being equally essential
to the function as that of the former. In like manner the tender and
delicate substance of the brain and spinal cord, the central seat of
the animal life, with which all the senses are in intimate communion,
is protected by bones and muscles which perform important voluntary
movements while the organs of sense which put us in connexion with the
external world, which render us susceptible of pleasure, and which
give us notice of the approach of objects capable of exciting pain,
are placed where external bodies may be brought most conveniently
and completely into contact with them; and where alone they can be
efficient as the sentinels of the system. For this reason, with the
exception of the sense of touch, which, though placed especially at the
extremities of the fingers, is also diffused over the whole external
surface of the frame, all the senses have their several seats in the
head, the most elevated part of the body, of an ovoid figure, capable
of moving independently of the rest of the fabric, and which, being
supported on a pivot, is enabled to describe at least two-thirds of a
circle.

Such is the difference in the structure and position of the apparatus
of the two lives, but the difference in their action is still more
striking.

1. The action of the apparatus of the organic life when sound is
without consciousness; the object of the action of the apparatus of
the animal life is the production of consciousness. The final cause
of the action of the apparatus of the organic life is the maintenance
of existence; the final cause of the action of the apparatus of the
animal life is the production of conscious existence. What purpose
would be answered by connecting consciousness with the action of
the organic organs? Were we sensible of the organic processes; did
we know when the heart beats, and the lung plays, and the stomach
digests, and the excretory organ excretes, the consciousness could
not promote, but might disturb the due and orderly course of these
processes. Moreover they would so occupy and engross our minds that
we should have little inclination or time to attend to other objects.
Beneficently therefore are they placed equally beyond our observation
and control. Nevertheless, when our consciousness of these processes
may be of service; when they are going wrong; when their too feeble or
too intense action is in danger of destroying existence, the animal
life is made sensible of what is passing in the organic, in order that
the former may take beneficial cognizance of the latter, may do what
experience may have taught to be conducive to the restoration of the
diseased organ to a sound state, or avoid doing what may conduce to the
increase or maintenance of its morbid condition.

But while the action of the organic organs is thus kept alike from our
view and feeling, the sole object of the action of the animal organs is
to produce and maintain a state of varied and extended consciousness.
We do not know when the heart dilates to receive the vital current,
nor when it contracts to propel it with renewed impetus through the
system; nor when the blood rushes to the lung to give out its useless
and noxious particles; nor when the air rushes to the blood to take
up those particles, to replace them by others, and thus to purify and
renovate the vital fluid. Many processes of this kind are continually
going on within us during every moment of our existence, but we are
no more conscious of them than we are of the motion of the fluids in
the blade of grass on which we tread. On the contrary when an external
object produces, in a sentient nerve, that change of state which we
denote by the words "an impression;" when the sentient nerve transmits
this impression to the brain; when the brain is thereby brought into
the state of perception, the animal life is in active operation, and
percipient or conscious existence takes place. Consciousness does not
belong to the organic, it _is_ the animal life.

2. The functions of the organic life are performed with uninterrupted
continuity; to those of the animal life rest is indispensable. The
action of the heart is unceasing; it takes not and needs not rest.
On it goes, for the space of eighty or ninety years, at the rate of
a hundred thousand strokes every twenty-four hours, having at every
stroke a great resistance to overcome, yet it continues this action for
this length of time without intermission. Alike incessant is the action
of the lung, which is always receiving and always emitting air; and the
action of the skin, which is always transpiring and always absorbing;
and the action of the alimentary canal, which is always compensating
the loss which the system is always sustaining.

But of this continuity of action the organs and functions of the
animal life are incapable. No voluntary muscle can maintain its action
beyond a given time; no effort of the will can keep it in a state of
uninterrupted contraction; relaxation must alternate with contraction;
and even this alternate action cannot go on long without rest. No organ
of sense can continue to receive impression after impression without
fatigue. By protracted exertion the ear loses its sensibility to sound,
the eye to light, the tongue to savour, and the touch to the qualities
of bodies about which it is conversant. The brain cannot carry on
its intellectual operations with vigour beyond a certain period; the
trains of ideas with which it works become, after a time, indistinct
and confused; nor is it capable of reacting with energy until it
has remained in a state of rest proportioned to the duration of its
preceding activity.

And this rest is sleep. Sleep is the repose of the senses, the rest of
the muscles, their support and sustenance. What food is to the organic,
sleep is to the animal life. Nutrition can no more go on without
aliment, than sensation, thought, and motion without sleep.

But it is the animal life only that sleeps: death would be the
consequence of the momentary slumber of the organic. If, when the brain
betook itself to repose, the engine that moves the blood ceased to
supply it with its vital fluid, never again would it awake. The animal
life is active only during a portion of its existence; the activity of
the organic life is never for a moment suspended; and in order to endow
its organs with the power of continuing this uninterrupted action,
they are rendered incapable of fatigue: fatigue, on the contrary, is
inseparable from the action of the organs of the animal life; fatigue
imposes the necessity of rest, rest is sleep, and sleep is renovation.

3. Between all the functions of the organic life there is a close
relation and dependence. Without the circulation there can be no
secretion; without secretion, no digestion; without digestion, no
nutrition; without nutrition, no new supply of circulating matter,
and so through the entire circle. But the functions of the animal
life are not thus dependent on each other. One of the circle may be
disordered without much disturbance of the rest; and one may cease
altogether, while another continues in vigorous action. Sensation may
be lost, while motion continues; and the muscle may contract though it
cannot feel. One organ of sense may sleep while the rest are awake.
One intellectual faculty may be in operation while others slumber. The
muscle of volition may act, while there is no consciousness of will.
Even the organs of the voice and of progression may perform their
office while the sensorium is deeply locked in sleep.

4. The two lives are born at different periods, and the one is in
active operation before the other is even in existence. The first
action observable in the embryo is a minute pulsating point. It is the
young heart propelling its infant stream. Before brain, or nerve, or
muscle can be distinguished, the heart is in existence and in action;
that is, the apparatus of the organic function of the circulation is
built up and is in operation before there is any trace of an animal
organ. Arteries and veins circulate blood, capillary vessels receive
the vital fluid, and out of it form brain and muscle, the organs of the
animal, no less than the various substances that compose the organs of
the organic life. The organic is not only anterior to the animal life,
but it is by the action of the organic that existence is given to the
animal life. The organic life is born at the first moment of existence;
the animal life not until a period comparatively distant; the epoch
emphatically called the period of birth, namely, the period when
the new being is detached from its mother; when it first comes into
contact with external objects; when it carries on all the functions
of its economy by its own organs, and consequently enjoys independent
existence.

5. The functions of the organic life are perfect at once. The heart
contracts as well, the arteries secrete as well, the respiratory
organs work as well the first moment they begin to act as at any
subsequent period. They require no teaching from experience, and they
profit nothing from its lessons. On the contrary, the operations
of the brain, and the actions of the voluntary muscles, feeble and
uncertain at first, acquire strength by slow degrees, and attain
their ultimate perfection only at the adult age. How indistinct
and confused the first sensations of the infant! Before it acquire
accuracy, precision, and truth, how immense the labour spent upon
perception! Sensations are succeeded by ideas; sensations and ideas
coalesce with sensations and ideas; combinations thus formed suggest
other combinations previously formed, and these a third, and the third
a fourth, and so is constituted a continuous train of thought. But
the infantile associations between sensation and sensation, between
idea and idea, and between sensations and ideas, are, to a certain
extent, incorrect, and to a still greater extent inadequate; and the
misconception necessarily resulting from this early imperfection in the
intellectual operations is capable of correction only by subsequent and
more extended impressions. During its making hours, a large portion of
the time of the infant is spent in receiving impressions which come
to it every instant from all directions, and which it stores up in
its little treasury; but a large portion is also consumed in the far
more serious and difficult business of discrimination and correction.
Could any man, after having attained the age of manhood, reverse the
order of the course through which he has passed; could he, with the
power of observation, together with the experience that belong to
manhood, retrace with perfect exactness every step of his sentient
existence, from the age of forty to the moment that the air first came
into contact with his body at the moment of his leaving his maternal
dwelling, among the truths he would learn, the most interesting, if
not the most surprising, would be those which relate to the manner in
which he dealt with his earliest impressions; with the mode in which
he combined them, recalled them, laid them by for future use; made his
first general deduction; observed what subsequent experience taught to
be conformable, and what not conformable, to this general inference;
his emotions on detecting his first errors, and his contrasted feelings
on discovering those comprehensive truths, the certainty of which
became confirmed by every subsequent impression. Thus to live backwards
would be, in fact, to go through the analysis of the intellectual
combinations, and, consequently, to obtain a perfect insight into the
constitution of the mind; and among the curious results which would
then become manifest, perhaps few would appear more surprising than the
true action of the senses. The eye, when first impressed by light, does
not perceive the objects that reflect it; the ear, when first impressed
by sound, does not distinguish the sonorous body. When the operation
for cataract has been successfully performed in a person born blind,
the eye immediately becomes sensible to light, but the impression of
light does not immediately give information relative to the properties
of bodies. It is gradually, not instantaneously; it is even by slow
degrees that luminous objects are discerned with distinctness and
accuracy. To see, to hear, to smell, to taste, to touch, are processes
which appear to be performed instantaneously, and which actually are
performed with astonishing rapidity in a person who observes them
in himself; but they were not always performed thus rapidly: they
are processes acquired, businesses learnt; processes and businesses
acquired and learnt, not without the cost of many efforts and much
labour. But the senses afford merely the materials for the intellectual
operations of memory, combination, comparison, discrimination,
induction, operations the progress of which is so slow, that they
acquire precision, energy, and comprehensiveness only after the culture
of years.

And the same is true of the muscles of volition. How many efforts are
made before the power of distinct articulation is acquired! how many
before the infant can stand! how many before the child can walk! The
organic life is born perfect; the animal life becomes perfect only by
servitude, and the aptitude which service gives.

6. The organic life may exist after the animal life has perished. The
animal life is extinguished when sensation is abolished, and voluntary
motion can be performed no more. But disease may abolish sensation and
destroy the power of voluntary motion, while circulation, respiration,
secretion, excretion, in a word, the entire circle of the organic
functions continues to be performed. In a single instant apoplexy may
reduce to drivelling fatuity the most exalted intellect, and render
powerless and motionless muscles of gigantic strength; while the action
of the heart and the involuntary contractions of the muscles may not
only not be weakened, but may act with preternatural energy. In a
single instant, apoplexy may even completely extinguish the animal
life, and yet the organic may go on for hours, days, and even weeks;
while catalepsy, perhaps the most singular disease to which the human
frame is subject, may wholly abolish sensation and volition, while
it may impart to the voluntary muscles the power of contracting with
such unnatural energy and continuity, that the head, the trunk, the
limbs may become immoveably fixed in whatever attitude they happen
to be at the moment the paroxysm comes on. In this extraordinary
condition of the nervous system, however long the paroxysm last, and
however complete the abolition of consciousness, the heart continues
to beat, and the pulse to throb, and the lungs to respire, and all the
organic organs to perform their ordinary functions. Dr. Jebb gives the
following description of the condition of a young lady who was the
subject of this curious malady.

"My patient was seized with an attack just as I was announced. At that
moment she was employed in netting; she was in the act of passing
the needle through the mesh; in that position she became immoveably
rigid, exhibiting, in a pleasing form, a figure of death-like sleep,
beyond the power of art to imitate, or the imagination to conceive.
Her forehead was serene, her features perfectly composed. The paleness
of her colour, and her breathing, which at a distance was scarcely
perceptible, operated in rendering the similitude to marble more exact
and striking. The position of her fingers, hands, and arms was altered
with difficulty, but preserved every form of flexure they acquired:
nor were the muscles of the neck exempted from this law, her head
maintaining every situation in which the hand could place it, as firmly
as her limbs."

In this condition of the system the senses were in a state of profound
sleep; the voluntary muscles, on the contrary, were in a state of
violent action; but this action not being excited by volition, nor
under its control, the patient remained as motionless as she was
insensible. The brain was in a state of temporary death; the muscle
in a state of intense life. And the converse may happen: the muscle
may die, while the brain lives; contractility may be destroyed, while
sensibility is perfect; the power of motion may be lost, while that of
sensation may remain unaffected. A case is on record, which affords
an illustration of this condition of the system. A woman had been for
some time confined to her bed, labouring under severe indisposition.
On a sudden she was deprived of the power of moving a single muscle of
the body; she attempted to speak, but she had no power to articulate;
she endeavoured to stretch out her hand, but her muscles refused to
obey the commands of her will, yet her consciousness was perfect, and
she retained the complete possession of her intellectual faculties.
She perceived that her attendants thought her dead, and was conscious
of the performance upon her own person of the services usually paid to
the dead; she was laid out, her toes were bound together, her chin was
tied up; she heard the arrangements for her funeral discussed, and yet
she was unable to make the slightest sign that she was still in the
possession of sense, feeling, and life.

In one form of disease, then, the animal life, both the sensitive and
the motive portions of it, may perish; and in another form of disease,
either the one or the other part of it may be suspended, while the
organic life continues in full operation: it follows that the two
lives, blended as they are, are distinct, since the one is capable of
perishing without immediately and inevitably involving the destruction
of the other.

7. And, finally, as the organic life is the first born, so it is the
last to die; while the animal life, as it is the latest born, and
the last to attain its full development, so it is the earliest to
decline and the first to perish. In the process of natural death, the
extinction of the animal is always anterior to that of the organic
life. Real death is a later, and sometimes a much later event than
apparent death. An animal appears to be dead when, together with the
abolition of sensation and the loss of voluntary motion, respiration,
circulation, and the rest of the organic functions can no longer be
distinguished; but these functions go on some time after they have
ceased to afford external indications of their action. In man, and the
warmblooded animals in general, suspension or submersion extinguishes
the animal life, at the latest, within the space of four minutes from
the time that the atmospheric air is completely excluded from the
lung; but did the organic functions also cease at the same period, it
would be impossible to restore an animal to life after apparent death
from drowning and the like. But however complete and protracted the
abolition of the animal functions, re-animation is always possible as
long as the organic organs are capable of being restored to their usual
vigour. The cessation of the animal life is but the first stage of
death, from which recovery is possible; death is complete only when the
organic together with the animal functions have wholly ceased, and are
incapable of being re-established.

In man, the process of death is seldom altogether natural. It is
generally rendered premature by the operation of circumstances which
destroy life otherwise than by that progressive and slow decay which is
the inevitable result of the action of organized structure. Death, when
natural, is the last event of an extended series, of which the first
that is appreciable is a change in the animal life and in the noblest
portion of that life. The higher faculties fail in the reverse order of
their development; the retrogression is the inverse of the progression,
and the noblest creature, in returning to the state of non-existence,
retraces step by step each successive stage by which it reached the
summit of life.

In the advancing series, the animal is superadded to the organic
life; sensation, the lowest faculty of the animal life, precedes
ratiocination, the highest. The senses called into play at the moment
of birth soon acquire the utmost perfection of which they are capable;
but the intellectual faculties, later developed, are still later
perfected, and the highest the latest.

In the descending series, the animal life fails before the organic, and
its nobler powers decay sooner and more rapidly than the subordinate.
First of all, the impressions which the organs of sense convey to
the brain become less numerous and distinct, and consequently the
material on which the mind operates is less abundant and perfect; but
at the same time, the power of working vigorously with the material it
possesses more than proportionally diminishes. Memory fails; analogous
phenomena are less readily and less completely recalled by the presence
of those which should suggest the entire train; the connecting links
are dimly seen or wholly lost; the train itself is less vivid and less
coherent; train succeeds train with preternatural slowness, and the
consequence of these growing imperfections is that, at last, induction
becomes unsound just as it was in early youth; and for the same
reason, namely, because there is not in the mental view an adequate
range of individual phenomena; the only difference being that the
range comprehended in the view of the old man is too narrow, because
that which he had learnt he has forgotten; while in the youth it is
too narrow, because that which it is necessary to learn has not been
acquired.

And with the diminution of intellectual power the senses continue
progressively to fail: the eye grows more dim, the ear more dull, the
sense of smell less delicate, the sense of touch less acute, while
the sense of taste immediately subservient to the organic function of
nutrition is the last to diminish in intensity and correctness, and
wholly fails but with the extinction of the life it serves.

But the senses are not the only servants of the brain; the voluntary
muscles are so equally; but these ministers to the master-power, no
longer kept in active service, the former no longer employed to convey
new, varied, and vivid impressions, the latter no longer employed
to execute the commands of new, varied, and intense desires, become
successively feebler, slower, and more uncertain in their action.
The hand trembles, the step totters, and every movement is tardy and
unsteady. And thus, by the loss of one intellectual faculty after
another, by the obliteration of sense after sense, by the progressive
failure of the power of voluntary motion; in a word, by the declining
energy and the ultimate extinction of the animal life, man, from the
state of maturity, passes a second time through the stage of childhood
back to that of infancy; lapses even into the condition of the embryo:
what the fœtus was, the man of extreme old age is: when he began to
exist, he possessed only organic life; and before he is ripe for the
tomb, he returns to the condition of the plant.

And even this merely organic existence cannot be long maintained. Slow
may be the waste of the organic organs; but they do waste, and that
waste is not repaired, and consequently their functions languish, and
no amount of stimulus is capable of invigorating their failing action.
The arteries are rigid and cannot nourish; the veins are relaxed and
cannot carry on the mass of blood that oppresses them; the lungs,
partly choked up by the deposition of adventitious matter, and partly
incapable of expanding and collapsing by reason of the feeble action
of the respiratory apparatus, imperfectly aërate the small quantity
of blood that flows through them; the heart, deprived of its wonted
nutriment and stimulus, is unable to contract with the energy requisite
to propel the vital current; the various organs, no longer supplied
with the quantity and quality of material necessary for carrying on
their respective processes, cease to act; the machinery stops, and this
is death.

And now the processes of life at an end, the body falls within the
dominion of the powers which preside universally over matter; the tie
that linked all its parts together, holding them in union and keeping
them in action, in direct opposition to those powers dissolved, it
feels and obeys the new attractions to which it has become subject;
particle after particle that stood in beautiful order fall from their
place; the wonderful structures they composed melt away; the very
substances of which those structures were built up are resolved into
their primitive elements; these elements, set at liberty, enter into
new combinations, and become constituent parts of new beings; those new
beings in their turn perish; from their death springs life, and so the
changes go on in an everlasting circle.

As far as relates to the organized structures in which life has its
seat, and to the operations of life dependent on those structures,
such is its history; a history not merely curious, but abounding with
practical suggestions of the last importance. The usefulness of a
familiar acquaintance with the phenomena which have now been elucidated
will be apparent at every step as we proceed.




CHAPTER III.

  Ultimate object of organization and life—Sources of
  pleasure—Special provision by which the organic organs
  influence consciousness and afford pleasure—Point at which
  the organic organs cease to affect consciousness, and
  why—The animal appetites: the senses: the intellectual
  faculties: the selfish and sympathetic affections: the
  moral faculty—Pleasure the direct, the ordinary, and the
  gratuitous result of the action of the organs—Pleasure
  conducive to the development of the organs, and to
  the continuance of their action—Progress of human
  knowledge—Progress of human happiness.


The object of structure is the production of function. Of the two
functions combined in the living animal, one is wholly subservient
to the other. To build up the apparatus of the animal life, and to
maintain it in a condition fit for performing its functions, is the
sole object of the existence of the organic life. What then is the
object of the animal life? That object, whatever it be, must be the
ultimate end of organization, and of all the actions of which it is the
seat and the instrument.

Two functions, sensation and voluntary motion, are combined in the
animal life. Of these two functions, the latter is subservient to the
former: voluntary motion is the servant of sensation, and exists only
to obey its commands.

Is sensation, then, the ultimate object of organization? Simple
sensation cannot be an ultimate object, because it is invariably
attended with an ultimate result; for sensation is either pleasurable
or painful. Every sensation terminates in a pleasure or a pain.
Pleasure or pain, the last event in the series, must then be the final
end.

Is the production of pain the ultimate object of organization? That
cannot be, for the production of pain is the indirect, not the
direct,—the extraordinary, not the ordinary, result of the actions
of life. It follows that pleasure must be the ultimate object, for
there is no other of which it is possible to conceive. The end of
organic existence is animal existence; the end of animal existence
is sentient existence; the end of sentient existence is pleasurable
existence; the end of life therefore is enjoyment. Life commences with
the organic processes; to the organic are superadded the animal; the
animal processes terminate in sensation; sensation ends in enjoyment;
it follows, that enjoyment is the final end. For this every organ is
constructed; to this every action of every organ is subservient; in
this every action ultimately terminates.

And without a single exception in the entire range of the sentient
creation, the higher the organized structure the greater the enjoyment,
mediately or immediately, to which it is subservient. From its most
simple to its most complex state, every successive addition to
structure, by which function is rendered more elevated and perfect,
proportionally increases the exquisiteness of the pleasure to which the
function ministers, and in which it terminates.

Pleasure is the result of the action of living organs, whether
organic or animal; pleasure is the direct, the ordinary, and the
gratuitous result of the action of both sets of organs; the pleasure
resulting from the action of the organs is conducive to their complete
development, and thereby to the increase of their capacity for
affording enjoyment; the pleasure resulting from the action of the
organs, and conducive to their development, is equally conducive to the
perpetuation of their action, and consequently to the maintenance of
life; it follows not only that enjoyment is the end of life, but that
it is the means by which life is prolonged. Of the truth of each of
these propositions, it will be interesting to contemplate the plenitude
of the proof.

1. In the first place, pleasure is the result of the action of the
organic organs. It has indeed been shown that the very character by
which the action of these organs is distinguished is that they are
unattended with consciousness. Nevertheless, by a special provision,
consciousness is indirectly connected with the processes of this
class, limited in extent indeed, and uniformly terminating at a
certain point; but the extent and the limitation alike conducing to
the pleasurableness of its nature. And this is an adjustment in the
constitution of our frame which is well deserving of attention.

Organic processes are dependent on a peculiar influence derived from
that portion of the nervous system distinguished by the term organic.
The organic nerves, distributed to the organic organs, take their
origin and have their chief seat in the cavities that contain the main
instruments of the organic life, namely, the chest and abdomen (see
chap. v.). As will be fully shown hereafter, these nerves encompass
the great trunks of the blood-vessels that convey arterial blood
to the organic organs. In all its ramifications through an organic
organ, an arterial vessel is accompanied by its organic nerve; so that
wherever the capillary arterial branch goes, secreting or nourishing,
there goes, inseparably united with it, an organic nerve, exciting and
governing.

Among the peculiarities of this portion of the nervous system, one
of the most remarkable is, that it is wholly destitute of feeling.
Sensibility is inseparably associated with the idea commonly formed of
a nerve. But the nervous system consists of two portions, one presiding
over sensation and voluntary motion, hence called the sentient and
the motive portions; the other destitute of sensation, but presiding
over the organic processes, hence called the organic portion. If the
communication between the organic organ and the organic nerve be
interrupted, the function of the organ, whatever it be, is arrested.
Without its organic nerves, the stomach cannot secrete gastric juice;
the consequence is, that the aliment is undigested. Without its organic
nerves, the liver cannot secrete bile, the consequence is, that the
nutritive part of the aliment is incapable of being separated from its
excrementitious portion. The organic organ receives from its organic
nerve an influence, without which it cannot perform its function;
but the nerve belonging to this class neither feels nor communicates
feeling, and hence it imparts no consciousness of the operation of any
process dependent upon it. Yet there is not one of these processes that
does not exert a most important influence over consciousness. How? By a
special provision, as curious in its nature as it is important in its
result.

Branches of sentient nerves are transmitted from the animal to the
organic system, and from the organic to the animal; and an intimate
communication is established between the two classes. The inspection
of fig. XVI. will illustrate the mode in which this communication is
effected. A B represents a portion of the spinal cord (one of the
central masses of the sentient system), covered with its membranes. The
part here represented is a front view of that portion of the spinal
cord which belongs to the back, and which is technically called the
dorsal portion.

[Illustration: Fig. XVI.]

1, 2, 3, 4, 5, 6, 7, 8, 9, the second, &c. ribs with the corresponding
dorsal (sentient) nerves, _a_, _b_, _c_, _d_, _e_, _f_, _g_, _h_, going
out to supply their respective organs with sensation.

C D E, a portion of the main trunk of the organic (non-sentient) nerve,
commonly called the Great Sympathetic.

F G H, the membrane of the spinal cord cut open and exposing I K, the
spinal cord itself, L, the anterior branch of one of the dorsal nerves,
arising from the anterior surface of the spinal cord by several bundles
of fibres.

M, the posterior branch of the same nerve, arising in like manner from
the posterior surface of the spinal cord by several branches of fibres.

The anterior and posterior branches uniting to form one trunk N.

Two branches, P Q, sent off from the spinal (sentient) trunk to unite
with the organic (non-sentient) trunk.

R S T U V W, other branches of the sentient, connected with the
branches of the non-sentient nervous trunks in the same mode.

X Y, the main trunk of the sympathetic (non-sentient) nerve cut across
and turned aside, in order that the parts beneath it (P N) may be more
distinctly seen.

From this description, it is apparent that each sentient nerve,
before it goes out to the animal organs, to which it is destined to
communicate sensation, sends off two branches to the organic or the
non-sentient. These sentient nerves mix and mingle with the insensible
nerves; accompany them in their course to the organic organs, and
ramify with them throughout their substance. It is manifest, then,
that sentient nerves, that nerves not necessary to the organic
processes, having, as far as is known, nothing whatever to do with
those processes, enter as constituent parts into the composition of the
organic organs. What is the result? That organic organs are rendered
sentient; that organic processes, in their own nature insensible,
become capable of affecting consciousness. What follows? What is the
consciousness excited? Not a consciousness of the organic process.
Of that we still remain wholly insensible. Not simple sensation. The
result uniformly produced, as long as the state of the system is that
of health, is pleasurable consciousness. The heart sends out to the
organs its vital current. Each organ, abstracting from the stream the
particles it needs, converts them into the peculiar fluid or solid
it is its office to form. The stomach, from the arterial streamlets
circulating through it, secretes gastric juice; the liver, from the
venous streamlets circulating through it, secretes bile. When these
digestive organs have duly prepared their respective fluids, they
employ them in the elaboration of the aliment. We are not conscious
of this elaboration, though it go on within us every moment; but is
consciousness not affected by the process? Most materially. Why?
Because sentient mingle with organic nerves; because the sentient
nerves are impressed by the actions of the organic organs. And how
impressed? As long as the actions of the organic organs are sound,
that is, as long as their processes are duly performed, the impression
communicated to the sentient nerves is in its nature agreeable; is,
in fact, THE PLEASURABLE CONSCIOUSNESS WHICH CONSTITUTES THE FEELING
OF HEALTH. The state of health is nothing but the result of the
due performance of the organic organs: it follows that the feeling
of health, the feeling which is ranked by every one among the most
pleasurable of existence, is the result of the action of organs of
whose direct operations we are unconscious. But the pleasurable
consciousness thus indirectly excited is really the consequence of a
special provision, established for the express purpose of producing
pleasure. Processes, in their own nature insensible, are rendered
sentient expressly for this purpose, that, over and above the special
object they serve, they may afford enjoyment. In this case, the
production of pleasure is not only altogether gratuitous, not only
communicated for its own sake, not only rested in as an ultimate
object, but it is made to commence at the very confines of life; it is
interwoven with the thread of existence: it is secured in and by the
actions that build up and that support the very framework, the material
instrument of our being.

But if the communication of sensibility to processes in their own
nature incapable of exciting feeling, for the purpose of converting
them into sources of pleasurable consciousness, indicate an express
provision for the production of enjoyment, that provision is no less
exemplified in the point at which this superadded sensibility is made
to cease.

Some of the consequences of a direct communication of consciousness
to an organic process have been already adverted to. Had the eye,
besides transmitting rays of light to the optic nerve, been rendered
sensible of the successive passage of each ray through its substance,
the impression excited by luminous bodies, which is indispensable to
vision, the ultimate object of the instrument, if not wholly lost,
must necessarily have become obscure, in direct proportion to the
acuteness of this sensibility. The hand of the musician could scarcely
have executed its varied and rapid movements upon his instrument, had
his mind been occupied at one and the same instant with the process
of muscular contraction in the finger, and the idea of music in the
brain. Had the communication of such a twofold consciousness been
possible, in no respect would it have been beneficial, in many it would
have been highly pernicious; and the least of the evils resulting
from it would have been, that the inferior would have interrupted the
superior faculty, and the means deteriorated the end. But in some
cases the evil would have been of a much more serious nature. Had we
been rendered sensible of the flow of the vital current through the
engine that propels it; were the distension of the delicate valves that
direct the current ever present to our view; by some inward feeling
were we reminded, minute by minute, of the progress of the aliment
through the digestive apparatus, and were the mysterious operations
of the organic nerves palpable to sight, the terror of the maniac,
who conceived that his body was composed of unannealed glass, would
be the ordinary feeling of life. Every movement would be a matter of
anxious deliberation; and the approach of every body to our own would
fill us with dismay. But adjusted as our consciousness actually is,
invariably the point at which the organic process begins is that at
which sensation ends. Had sensation been extended beyond this point, it
would have been productive of pain: at this point it uniformly stops.
Nevertheless, by the indirect connexion of sensation with the organic
processes, a vast amount of pleasure might be created: a special
apparatus is constructed for the express purpose of establishing the
communication. There is thus the twofold proof, the positive and the
negative, the evidence arising as well from what they do, as from
what they abstain from doing, that the organic processes are, and are
intended to be, sources of enjoyment.

But the production of pleasure, commencing at this the lowest point
of conscious existence, increases with the progressive advancement of
organization and function.

The appetite for food, and the voluntary actions dependent upon it,
may be considered as the first advancement beyond a process purely
organic. The function by which new matter is introduced into the
system and converted into nutriment, is partly an animal and partly an
organic operation. The animal part of it consists of the sensations of
hunger and thirst, by which we are taught when the wants of the system
require a fresh supply of aliment, together with the voluntary actions
by which the aliment is introduced into the system. The organic part
of the function consists of the changes which the aliment undergoes
after its introduction into the system, by which it is converted into
nutriment. Sensations always of a pleasurable nature arise indirectly
in the manner already explained, from the due performance of the
organic part of the function; but pleasure is also directly produced by
the performance of the animal part of it. Wholesome food is grateful;
the satisfaction of the appetite for food is pleasurable. Food is
necessary to the support of life; but it is not indispensable to the
maintenance of life that food should be agreeable. Appetite there
must be, that food may be eaten; but the act of eating might have
been secured without connecting it with pleasure. Pleasure, however,
is connected with it, first directly, by the gratefulness of food,
and secondly indirectly, by the due digestion of the food. And the
annexation of pleasure in this twofold mode to the performance of the
function of nutrition is another case of the gratuitous bestowment of
pleasure; another instance in which pleasure is communicated for its
own sake, and rested in as an ultimate object. Pleasures of this class
are sometimes called low; they are comparatively low; but they are not
the less pleasures, because they are exceeded in value by pleasures of
a nobler nature. Man may regard them with comparative indifference,
because he is endowed with faculties which afford him gratifications
superior in kind and larger in amount; but it is no mark of wisdom to
despise and neglect even these: for they are annexed to the exercise
of a function which is the first to exalt us above a merely organic
existence; they are the first pleasures of which, considered merely as
sentient creatures, we are susceptible; they amount in the aggregate to
an immense sum; and they mark the depth in our nature in which are laid
the fountains of enjoyment.

Organs of sense, intellectual faculties, social affections, moral
powers, are superadded endowments of a successively higher order:
at the same time, they are the instruments of enjoyment of a nature
progressively more and more exquisite.

An organ of sense is an instrument composed of a peculiar arrangement
of organized matter, by which it is adapted to receive from specific
agents definite impressions. Between the agent that produces and the
organ that receives the impression, the adaptation is such, that the
result of their mutual action is, in the first place, the production of
sensation, and, in the second place, the production of pleasure. The
pleasure is as much the result as the sensation. This is true of the
eye in seeing, the ear in hearing, the hand in touching, the organ of
smell in smelling, and the tongue in tasting. Pleasure is linked with
the sense; but there might have been the sense without the pleasure.
A slight difference in the construction of the organ, or in the
intensity of the agent, would not merely have changed, it would even
have reversed the result; would have rendered the habitual condition of
the eye, the ear, the skin, not such as it now is in health, but such
as it is in the state of inflammation. But the adjustment is such as
habitually to secure that condition of the system in which every action
that excites sensation produces pleasure as its ordinary concomitant;
and the amount of enjoyment which is thus secured to every man, and
which every man without exception actually experiences in the ordinary
course of an ordinary life, it would be beyond his power to estimate
were he always sensible of the boon; but the calculation is altogether
impossible, when, as is generally the case, he merely enjoys without
ever thinking of the provisions which enable him to do so.

But if the pleasures that arise from the ordinary operations of sense
form, in the aggregate, an incalculable sum, how great is the accession
brought to this stock by the endowments next in order in the ascending
scale, namely, the intellectual faculties!

There is one effect resulting from the operation of the intellectual
faculties on the senses that deserves particular attention. The higher
faculties elevate the subordinate in such a manner as to make them
altogether new endowments. In illustration of this, it will suffice
to notice the change wrought, as if in the very nature of sensation,
the moment it becomes combined with an intellectual operation, as
exemplified in the difference between the intellectual conception of
beauty, and the mere perception of sense. The grouping of the hills
that bound that magnificent valley which I behold at this moment spread
out before my view; the shadow of the trees at the base of some of
them, stretching its deep and varied outline up the sides of others;
the glancing light now brightening a hundred different hues of green
on the broad meadows, and now dancing on the upland fallows; the
ever-moving, ever-changing clouds; the scented air; the song of birds;
the still more touching music which the breeze awakens in the scarcely
trembling branches of those pine trees,—the elements of which this
scene is composed, the mere objects of sense, the sun, the sky, the
air, the hills, the woods, and the sounds poured out from them, impress
the senses of the animals that graze in the midst of them; but on their
senses they fall dull and without effect, exciting no perception of
their loveliness, and giving no taste of the pleasures they are capable
of affording. Nor even in the human being, whose intellectual faculties
have been uncultivated, do they awaken either emotions or ideas; the
clown sees them, hears them, feels them no more than the herds he
tends: yet in him whose mind has been cultivated and unfolded, how
numerous and varied the impressions, how manifold the combinations, how
exquisite the pleasures produced by objects such as these!

And from the more purely intellectual operations, from memory,
comparison, analysis, combination, classification, induction, how
still nobler the pleasure! Not to speak of the happiness of him who,
by his study of natural phenomena, at length arrived at the stupendous
discovery that the earth and all the stars of the firmament move, and
that the feather falls to the ground, by the operation of one and the
same physical law; nor of the happiness of him who sent his kite into
the cloud, and brought down from its quiet bed the lightning which
he suspected was slumbering there; nor of the happiness of him who
concentrated, directed, and controlled that mighty power which has
enabled the feeble hand of man to accomplish works greater than have
been feigned of fabled giant; which has annihilated distance; created,
by economizing time; changed in the short space in which it has been in
operation the surface of the habitable globe; and is destined to work
upon it more and greater changes than have been effected by all other
causes combined; nor of the happiness of him who devoted a longer life
with equal success to a nobler labour, that of REARING THE FABRIC OF
FELICITY BY THE HAND OF REASON AND OF LAW. The intellectual pleasures
of such men as Newton, Franklin, Watt, and Bentham, can be _equalled_
only by those who possess equal intellectual power, and who put forth
equal intellectual energy: to be greatly happy as they were, it were
necessary to be as highly endowed; but to be happy, it is not necessary
to be so endowed. In the ordinary intellectual operations of ordinary
men, in their ordinary occupations, there is happiness. Every human
being whose moments have passed with winged speed, whose day has been
short, whose year is gone almost as soon as it seemed commenced, has
derived from the exercise of his intellectual faculties pleasures
countless in number and inestimable in value.

But the sympathetic pleasures, out of which grow the social, are of
a still higher order even than the intellectual. The pleasures that
result from the action of the organic organs, from the exercise of the
several senses, and from the operation of the intellectual faculties,
like the sensations in which they arise, belong exclusively to the
individual being that experiences them, and cannot be communicated
to another. Similar sensations and pleasures may be felt by beings
similarly constituted; but the actual sensations and pleasures afforded
by the exercise of a person's own organs and faculties are no more
capable of becoming another's than his existence. These, then, are
strictly the selfish pleasures; and the provision that has been made
for securing them has been shown.

But there are pleasures of another class, pleasures having no relation
whatever to a person's own sensation or happiness; pleasures springing
from the perception of the enjoyment of others. The sight of pleasure
not its own affects the human heart, provided its state of feeling be
natural and sound, just as it would be affected were it its own. Not
more real is the pleasure arising from the gratification of appetite,
the exercise of sense, and the operation of intellect, than that
arising from the consciousness that another sentient being is happy.
Pleasures of this class are called sympathetic, in contradistinction to
those of the former class, which are termed selfish.

There are then two principles in continual operation in the human
being, the selfish and the sympathetic. The selfish is productive of
pleasure of a certain kind; the sympathetic is productive of pleasure
of another kind. The selfish is primary and essential; the sympathetic,
arising out of the selfish, is superadded to it. And so precisely
what the animal life is to the organic, the sympathetic principle is
to the selfish; and just what the organic life gains by its union
with the animal, the mental constitution gains by the addition of
the sympathetic to the selfish affection. The analogy between the
combination in both cases is in every respect complete. As the organic
life produces and sustains the animal, so the sympathetic principle
is produced and sustained by the selfish. As the organic life is
conservative of the entire organization of the body, so the selfish
principle is conservative of the entire being. As the animal life is
superadded to the organic, extending, exalting, and perfecting it,
so the sympathetic principle is superadded to the selfish, equally
extending, exalting, and perfecting it. The animal life is nobler than
the organic, whence the organic is subservient to the animal; but there
is not only no opposition, hostility, or antagonism between them, but
the strictest possible connexion, dependence, and subservience. The
sympathetic principle is nobler than the selfish, whence the selfish is
subservient to the sympathetic; but there is not only no opposition,
hostility, or antagonism between them, but the strictest possible
connexion, dependence, and subservience. Whatever is conducive to the
perfection of the organic, is equally conducive to the perfection of
the animal life; and whatever is conducive to the attainment of the
true end of the selfish is equally conducive to the attainment of the
true end of the sympathetic principle. The perfection of the animal
life cannot be promoted at the expense of the organic, nor that of the
organic at the expense of the animal; neither can the ultimate end of
the selfish principle be secured by the sacrifice of the sympathetic,
nor that of the sympathetic by the sacrifice of the selfish. Any
attempt to exalt the animal life beyond what is compatible with the
healthy state of the organic, instead of accomplishing that end, only
produces bodily disease. Any attempt to extend the selfish principle
beyond what is compatible with the perfection of the sympathetic,
or the sympathetic beyond what is compatible with the perfection of
the selfish, instead of accomplishing the end in view, only produces
mental disease. Opposing and jarring actions, antagonizing and mutually
destructive powers, are combined in no other work of nature; and it
would be wonderful indeed were the only instance of it found in man,
the noblest of her works, and in the mind of man, the noblest part of
her noblest work.

No one supposes that there is any such inharmonious combination in
the organization of his physical frame, and the notion that it exists
in his mental constitution, as it is founded in the grossest ignorance,
so it is productive of incalculable mischief. In both, indeed, are
manifest two great powers, each distinct; each having its own peculiar
operation; and the one being subservient to the other, but both
conducing alike to one common end. By the addition of the apparatus of
the animal to that of the organic life, a nobler structure is built
up than could have been framed by the organic alone: by the addition
of the sympathetic to the selfish part of the mental constitution, a
happier being is formed than could have been produced by the selfish
alone. And as the organic might have existed without the animal life,
but by the addition of the animal a new and superior being is formed,
so might the selfish part of the mental constitution, and the pleasures
that flow from it, have existed alone; but by the addition of the
sympathetic, a sum is added to enjoyment, of the amount of which some
conception may be formed by considering what human life would be, with
every selfish appetite and faculty gratified in the fullest conceivable
degree, but without any admixture whatever of sympathetic or social
pleasure. Selfish enjoyment is not common. If any one set himself to
examine what at first view might seem a purely selfish pleasure, he
will soon be sensible that, of the elements composing any given state
of mind to which he would be willing to affix the term pleasurable,
a vast preponderance consists of sympathetic associations. The more
accurately he examine, and the farther he carry his analysis, the
stronger will become his conviction, that a purely selfish enjoyment,
that is, a truly pleasurable state of mind, in no degree, mediately or
immediately, connected with the pleasurable state of another mind, is
exceedingly rare.

But if the constitution of human nature and the structure of human
society alike render it difficult for the human heart to be affected
with a pleasure in no degree derived from—absolutely and totally
unconnected with sympathetic association, of that complex pleasure
which arises out of social intercourse, partly selfish and partly
sympathetic, how far sweeter the sympathetic than the selfish
part; and as the sympathetic preponderates over the selfish, how
vast the increase of the pleasure! And when matured, exalted into
affection—affection, that holy emotion which exerts a transforming
influence over the selfish part of human nature, turning it into the
sympathetic; affection, which renders the happiness of the beloved
object inexpressibly dearer to the heart than its own; affection,
among the benignant feelings of which as there is none sweeter so
there is none stronger than that of self-devotion, nay, sometimes even
of self-sacrifice; affection, which is sympathy pure, concentrated,
intense—Oh how beautiful is the constitution of this part of our
nature, by which the most transporting pleasures the heart receives are
the direct reflection of those it gives!

Nor ought it to be overlooked, that, while nearly all the selfish,
like all the sensual pleasures, cannot be increased beyond a fixed
limit, cannot be protracted beyond a given time, are short-lived in
proportion as they are intense, and satiate the appetite they gratify,
the sympathetic pleasures are capable of indefinite augmentation; are
absolutely inexhaustible; no limit can be set to their number, and no
bound to their growth; they excite the appetite they gratify; they
multiply with and by participation, and the more is taken from the
fountain from which they flow, the deeper, the broader, and the fuller
the fountain itself becomes.

But not only is the mental state of affection in all its forms and
degrees highly pleasurable, but the very consciousness of being the
object of affection is another pleasure perfectly distinct from that
arising immediately from the affection itself. It has been said of
charity, that it is twice blessed, that it blesses alike him that
gives and him that receives; but love has in it a threefold blessing:
first, in the mental state itself; secondly, in the like mental state
which the manifestation of it produces in another; and thirdly, in the
mental state inseparable from the consciousness of being the object of
affection. And this reflex happiness, this happiness arising from the
consciousness of being the object, is even sweeter than any connected
with being the subject of affection.

In like manner there is pleasure in the performance of beneficent
actions; in energetic, constant, and therefore ultimately successful
exertions to advance the great interests of human kind, in art, in
science, in philosophy, in education, in morals, in legislation,
in government; whether those exertions are put forth in the study,
the school, the senate, or any less observed though perhaps not
less arduous nor less important field of labour. Exertions of this
kind beget in those for whom, towards those by whom, they are made,
benignant feelings—respect, veneration, gratitude, love. With
such feelings the philosopher, the instructor, the legislator, the
statesman, the philanthropist, knows that he is, or that, sooner or
later, he will be regarded by his fellow men; and in this consciousness
there is happiness: but this is another source of happiness perfectly
distinct from that arising from the performance of beneficent actions;
it is a new happiness superadded to the former, and, if possible,
still more exquisite. Thus manifold is the beneficent operation of the
sympathetic affection: thus admirable is the provision made in the
constitution of our nature for the excitement and extension of this
affection, and, through its instrumentality, for the multiplication and
exaltation of enjoyment!

In affections and actions of the class just referred to, and in the
pleasures that result from them, there is much of the nature which is
commonly termed moral. And the power to which the moral affections and
actions are referred is usually and justly considered as the supreme
faculty of the mind; for it is the regulator and guide of all the
others; it is that by which they attain their proper and ultimate
object. Of whatever pleasure human nature is capable in sensation, in
idea, in appetite, in passion, in emotion, in affection, in action;
whatever is productive of real pleasure, in contradistinction to what
only cheats with the false hope of pleasure; whatever is productive
of pure pleasure, in contradistinction to what is productive partly
of pleasure and partly of pain, and consequently productive not of
pure, but of mixed pleasure; whatever is productive of a great degree
of pleasure in contradistinction to what is productive of a small
degree of pleasure; whatever is productive of lasting pleasure, in
contradistinction to what is productive of temporary pleasure; whatever
is productive of ultimate pleasure, in contradistinction to what is
productive of immediate pleasure, but ultimate pain; this greatest and
most perfect pleasure it is the part of the moral faculty to discover.
In the degree in which the operation of this faculty is correct and
complete, it enables the human being to derive from every faculty of
his nature the greatest, the purest, the most enduring pleasure; that
is, the maximum of felicity. This is the proper scope and aim of the
moral faculty; to this its right exercise is uniformly conducive; and
this, as it is better cultivated and directed, it will accomplish in
a higher degree, in a continual progression, to which no limit can
be assigned. But if the operation of this faculty be to render every
other in the highest degree conducive to happiness, conformity to
the course of conduct required by it, must of course be that highest
happiness. Conformity to the course of conduct pointed out by the
moral faculty as conducive in the highest degree to happiness is moral
excellence, or, in the definite and exact sense of the word, virtue.
And in this sense it is that virtue is happiness. It is because it
discriminates the true sources of happiness, that is, directs every
other faculty into its proper course, and guides it in that course to
the attainment of its ultimate object, that the moral faculty is ranked
as the highest faculty of the mind. Supposing the operation of this
faculty to be perfect, it is but an identical expression to say, that
to follow its guidance implicitly is to follow the road that leads to
the most perfect happiness. But, over and above the happiness thus
directly and necessarily resulting from yielding uniform and implicit
obedience to the moral faculty, there is, in the very consciousness of
such conformity, a new happiness, as pure as it is exalted. Thus, in
a twofold manner, is the moral the highest faculty of the mind, the
source of its highest happiness; and thus manifest it is, from every
view that can be taken of the constitution of human nature, that every
faculty with which it is endowed, from the highest to the lowest, not
only affords its own proper and peculiar pleasure, but that each, as
it successively rises in the scale, is proportionately the source of a
nobler kind, and a larger amount of enjoyment.

And the pleasure afforded by the various faculties with which the human
being is endowed is the immediate and direct result of their exercise.
With the exception of the organic organs, and the reason for the
exception in regard to them has been assigned, the action of the organs
is directly pleasurable. From the exercise of the organs of sense, from
the operation of the intellectual faculties, from appetite, passion,
and affection, pleasure flows as directly as the object for which the
instrument is expressly framed.

And pleasure is the ordinary result of the action of the organs; pain
is sometimes the result, but it is the extraordinary not the ordinary
result. Whatever may be the degree of pain occasionally produced, or
however protracted its duration, yet it is never the natural, that
is, the usual or permanent state, either of a single organ, or of an
apparatus, or of the system. The usual, the permanent, the natural
condition of each organ, and of the entire system, is pleasurable.
Abstracting, therefore, from the aggregate amount of pleasure, the
aggregate amount of pain, the balance in favour of pleasure is immense.
This is true of the ordinary experience of ordinary men, even taking
their physical and mental states such as they are at present; but the
ordinary physical and mental states, considered as sources of pleasure
of every human being, might be prodigiously improved; and some attempt
will be made, in a subsequent part of this work, to show in what manner
and to what extent.

It has been already stated that there are cases in which pleasure is
manifestly given for its own sake; in which it is rested in as an
ultimate object: but the converse is never found: in no case is the
excitement of pain gratuitous. Among all the examples of secretion,
there is no instance of a fluid, the object of which is to irritate
and inflame: among all the actions of the economy, there is none, the
object of which is the production of pain.

Moreover, all such action of the organs, as is productive of pleasure,
is conducive to their complete development, and consequently to the
increase of their capacity for producing pleasure; while all such
action of the organs as is productive of pain is preventive of their
complete development, and consequently diminishes their capacity
for producing pain. The natural tendency of pleasure is to its own
augmentation and perpetuity. Pain, on the contrary, is self-destructive.

Special provision is made in the economy, for preventing pain
from passing beyond a certain limit, and from enduring beyond a
certain time. Pain, when it reaches a certain intensity, deadens the
sensibility of the sentient nerve; and when it lasts beyond a certain
time, it excites new actions in the organ affected, by which the organ
is either restored to a sound state, or so changed in structure that
its function is wholly abolished. But change of structure and abolition
of function, if extensive and permanent, are incompatible with the
continuance of life. If, then, the actions of the economy, excited by
pain, fail to put an end to suffering by restoring the diseased organ
to a healthy state, they succeed in putting an end to it by terminating
life. Pain, therefore, cannot be so severe and lasting as materially to
preponderate over pleasure, without soon proving destructive to life.

But the very reverse is the case with pleasure. All such action of the
organs as is productive of pleasure is conducive to the perpetuation
of life. There is a close connexion between happiness and longevity.
Enjoyment is not only the end of life, but it is the only condition
of life which is compatible with a protracted term of existence. The
happier a human being is, the longer he lives; the more he suffers,
the sooner he dies; to add to enjoyment, is to lengthen life; to
inflict pain, is to shorten the duration of existence. As there is a
point of wretchedness beyond which life is not desirable, so there is
a point beyond which it is not maintainable. The man who has reached
an advanced age cannot have been, upon the whole, an unhappy being;
for the infirmity and suffering which embitter life cut it short.
Every document by which the rate of mortality among large numbers of
human beings can be correctly ascertained contains in it irresistible
evidence of this truth. In every country, the average duration of life,
whether for the whole people or for particular classes, is invariably
in the direct ratio of their means of felicity; while, on the other
hand, the number of years which large portions of the population
survive beyond the adult age may be taken as a certain test of the
happiness of the community. How clear must have been the perception of
this in the mind of the Jewish legislator when he made the promise,
THAT THY DAYS MAY BE LONG IN THE LAND WHICH THE LORD THY GOD HATH GIVEN
THEE—the sanction of every religious observance, and the motive to
every moral duty!

Deeply then are laid the fountains of happiness in the constitution
of human nature. They spring from the depths of man's physical
organization; and from the wider range of his mental constitution
they flow in streams magnificent and glorious. It is conceivable that
from the first to the last moment of his existence, every human being
might drink of them to the full extent of his capacity. Why does he
not? The answer will be found in that to the following question. What
must happen before this be possible? The attainment of clear and just
conceptions on subjects, in relation to which the knowledge hitherto
acquired by the most enlightened men is imperfect. Physical nature,
every department of it, at least, which is capable of influencing
human existence and human sensation; human nature, both the physical
and the mental part of it; institutions so adapted to that nature
as to be capable of securing to every individual, and to the whole
community, the maximum of happiness with the minimum of suffering—this
must be known. But knowledge of this kind is of slow growth. To
expect the possession of it on the part of any man in such a stage of
civilization as the present, is to suppose a phenomenon to which there
is nothing analogous in the history of the human mind. The human mind
is equally incapable of making a violent discovery in any department of
knowledge, and of taking a violent bound in any path of improvement.
What we call discoveries and improvements are clear, decided, but
for the most part gentle, steps in advancement of the actual and
immediately-preceding state of knowledge. The human mind unravels the
great chain of knowledge, link by link; when it is no longer able to
trace the connecting link, it is at a stand; the discoverer, in common
with his contemporaries, seeing the last ascertained link, and from
that led on by analogies which are not perceived by, or which do not
impress, others, at length descries the next in succession; this brings
into view new analogies, and so prepares the way for the discernment
of another link; this again elicits other analogies which lead to the
detection of other links, and so the chain is lengthened. And no link,
once made out, is lost.

Chemists tell us that the adjustment of the component elements of
water is such, that although they readily admit of separation and are
subservient to their most important uses in the economy of nature
by this very facility of decomposition, yet that their tendency to
recombination is equal, so that the quantity of water actually existing
at this present moment in the globe is just the same as on the first
day of the creation, neither the operations of nature, nor the purposes
to which it has been applied by man, having used up, in the sense of
destroying, a single particle of it. Alike indestructible are the
separate truths that make up the great mass of human knowledge. In
their ready divisibility and their manifold applications, some of
them may sometimes seem to be lost; but if they disappear, it is only
to enter into new combinations, many of which themselves become new
truths, and so ultimately extend the boundaries of knowledge. Whatever
may have been the case in time past, when the loss of an important
truth, satisfactorily and practically established, may be supposed
possible, such an event is inconceivable now when the art of printing
at once multiplies a thousand records of it, and, with astonishing
rapidity, makes it part and parcel of hundreds of thousands of minds.
A thought more full of encouragement to those who labour for the
improvement of their fellow beings there cannot be. No onward step is
lost; no onward step is final; every such step facilitates and secures
another. The savage state, that state in which gross selfishness seeks
its object simply and directly by violence, is past. The semi-savage or
barbarous state, in which the grossness of the selfishness is somewhat
abated, and the violence by which it seeks its object in some degree
mitigated, by the higher faculties and the gentler affections of our
nature, but in which war still predominates, is also past. To this has
succeeded the state in which we are at present, the so-called civilized
state—a state in which the selfish principle still predominates, in
which the justifiableness of seeking the accomplishment of selfish
purposes by means of violence, that of war among the rest, is still
recognized, but in which violence is not the ordinary instrument
employed by selfishness, its ends being commonly accomplished by the
more silent, steady, and permanent operation of institutions. This
state, like the preceding, will pass away. How soon, in what precise
mode, by what immediate agency, none can tell. But we are already
in possession of the principle which will destroy the present and
introduce a better social condition, namely, the principle at the basis
of the social union, THE MAXIMUM OF THE AGGREGATE OF HAPPINESS; THE
MAXIMUM OF THE AGGREGATE OF HAPPINESS SOUGHT BY THE PROMOTION OF THE
MAXIMUM OF INDIVIDUAL HAPPINESS!




CHAPTER IV.

  Relation between the physical condition and happiness, and
  between happiness and longevity—Longevity a good, and
  why—Epochs of life—The age of maturity the only one that
  admits of extension—Proof of this from physiology—Proof
  from statistics—Explanation of terms—Life a fluctuating
  quantity—Amount of it possessed in ancient Rome: in modern
  Europe: at present in England among the mass of the people
  and among the higher classes.


Life depends on the action of the organic organs. The action of the
organic organs depends on certain physical agents. As each organic
organ is duly supplied with the physical agent by which it carries on
its respective process, and as it duly appropriates what it receives,
the perfection of the physical condition is attained; and, according to
the perfection or imperfection of the physical condition, supposing no
accident interrupt its regular course, is the length or the brevity of
life.

It is conceivable that the physical condition might be brought to a
high degree of perfection, the mind remaining in a state but little
fitted for enjoyment; because it is necessary to enjoyment that there
be a certain development, occupation, and direction of the mental
powers and affections: and the mental state may be neglected, while
attention is paid to the physical processes. But the converse is not
possible. The mental energies cannot be fully called forth while the
physical condition is neglected. Happiness presupposes a certain degree
of excellence in the physical condition; and unless the physical
condition be brought to a high degree of excellence, there can be no
such development, occupation, and direction of the mental powers and
affections as is requisite to a high degree of enjoyment.

That state of the system in which the physical condition is sound is
in itself conducive to enjoyment; while a permanent state of enjoyment
is in its turn conducive to the soundness of the physical condition.
It is impossible to maintain the physical processes in a natural and
vigorous condition if the mind be in a state of suffering. The bills
of mortality contain no column exhibiting the number of persons who
perish annually from bodily disease, produced by mental suffering;
but every one must occasionally have seen appalling examples of the
fact. Every one must have observed the altered appearance of persons
who have sustained calamity. A misfortune, that struck to the heart,
happened to a person a year ago; observe him some time afterwards; he
is wasted, worn, the miserable shadow of himself; inquire about him at
the distance of a few months, he is no more.

It is stated by M. Villermé, that the ordinary rate of mortality in
the prisons of France, taking all together, is one in twenty-three—a
rate which corresponds to the age of sixty-five in the common course
of life. But in the vast majority of cases the unfortunate victims
of the law are no older than from twenty-five to forty-five years of
age. Taking them at the mean age of thirty-five, it follows that the
suffering from imprisonment, and from the causes that lead to it, is
equivalent to thirty years wear and tear of life. But this is not all;
for it is found that, during imprisonment, the ordinary chances of
death are exactly quadrupled.

In regard to the whole population of a country, indigence may be
assumed to be a fair measure of unhappiness, and wealth of happiness.
If the rate of mortality in the indigent class be compared with that
of the wealthy, according to M. Villermé, it will be found in some
cases to be just double. Thus it is affirmed that, in some cases in
France, taking equal numbers, where there are one hundred deaths in a
poor arrondissement, there are only fifty in a rich; and that taking
together the whole of the French population, human life is protracted
twelve years and a half among the wealthy beyond its duration among
the poor: consequently, in the one class, a child, newly born, has a
probability of living forty-two and a half years; in the other only
thirty years.

In the great life-insurance establishments in England, a vast
proportion of the persons who insure their lives are persons compelled
to do so by their creditors; while three-fourths of those who
voluntarily insure their lives are professional men, living in great
towns, and experiencing the anxieties and fatigues, the hopes and
disappointments of professional life. In one of these establishments in
London, out of 330 deaths that happened in twenty-six years preceding
the year 1831, it was found that eleven died by suicide, being one
in thirty, implying the existence of an appalling amount of mental
suffering. The number of persons belonging to an insurance office who
perish by suicide is sure to be accurately known, death by suicide
rendering the policy void. It would be most erroneous to suppose that
these persons put an end to their existence under the mere influence of
the mental states of disappointment and despondency. The mind reacted
upon the body: produced physical disease, probably inflammation of the
brain, and under the excitement of this physical disease, the acts of
suicide were committed. More than one case has come to my knowledge
in which inflammation of the brain having been excited by mental
suffering, suicide was committed by cutting the throat. During the flow
of blood, which was gradual, the brain was relieved; the mind became
perfectly rational; and the patient might have been saved had a surgeon
been upon the spot, or had the persons about the patient known where
and how to apply the pressure of the finger to staunch the flow of
blood, until surgical aid could be procured.

By a certain amount and intensity of misery life may be suddenly
destroyed; by a smaller amount and intensity, it may be slowly worn out
and exhausted. The state of the mind affects the physical condition;
but the continuance of life is wholly dependent on the physical
condition: it follows that in the degree in which the state of the
mind is capable of affecting the physical condition, it is capable of
influencing the duration of life.

Were the physical condition always perfect, and the mental state always
that of enjoyment, the duration of life would always be extended to
the utmost limit compatible with that of the organization of the
body. But as this fortunate concurrence seldom or never happens,
human life seldom or never numbers the full measure of its days.
Uniform experience shows, however, that, provided no accident occur to
interrupt the usual course, in proportion as body and mind approximate
to this state, life is long; and as they recede from it, it is short.
Improvement of the physical condition affords a foundation for the
improvement of the mental state; improvement of the mental state
improves up to a certain point the physical condition; and in the ratio
in which this twofold improvement is effected, the duration of life
increases.

Longevity then is a good, in the first place, because it is a sign
and a consequence of the possession of a certain amount of enjoyment;
and in the second place, because this being the case, of course in
proportion as the term of life is extended, the sum of enjoyment must
be augmented. And this view of longevity assigns the cause, and shows
the reasonableness of that desire for long life which is so universal
and constant as to be commonly considered instinctive. Longevity and
happiness, if not invariably, are generally, co-incident.

If there may be happiness without longevity, the converse is not
possible: there cannot be longevity without happiness. Unless the state
of the body be that of tolerable health, and the state of the mind
that of tolerable enjoyment, long life is unattainable: these physical
and mental conditions no longer existing, nor capable of existing, the
desire of life and the power of retaining it cease together.

An advanced term of life and decrepitude are commonly conceived to
be synonymous: the extension of life is vulgarly supposed to be the
protraction of the period of infirmity and suffering, that period which
is characterized by a progressive diminution of the power of sensation,
and a consequent and proportionate loss of the power of enjoyment, the
"sans teeth, sans eyes, sans taste, sans every thing." But this is so
far from being true, that it is not within the compass of human power
to protract in any sensible degree the period of old age properly so
called, that is, the stage of decrepitude. In this stage of existence,
the physical changes that successively take place clog, day by day, the
vital machinery, until it can no longer play. In a space of time, fixed
within narrow limits, the flame of life must then inevitably expire,
for the processes that feed it fail. But though, when fully come, the
term of old age cannot be extended, the coming of the term may be
postponed. To the preceding stage, an indefinite number of years may be
added. And this is a fact of the deepest interest to human nature.

The division of human life into periods or epochs is not an arbitrary
distinction, but is founded on constitutional differences in the
system, dependent on different physiological conditions. The periods
of infancy, childhood, boyhood, adolescence, manhood, and old age, are
distinguished from each other by external characters, which are but
the outward signs of internal states. In physiological condition, the
infant differs from the child, the child from the boy, the boy from the
man, and the adult from the old man, as much in physical strength as in
mental power. There is an appointed order in which these several states
succeed each other; there is a fixed time at which one passes into
another. That order cannot be inverted: no considerable anticipation
or postponement of that fixed time can be effected. In all places and
under all circumstances, at a given time, though not precisely at the
same time in all climates and under all modes of life, infancy passes
into childhood, childhood into boyhood, boyhood into adolescence, and
adolescence into manhood. In the space of two years from its birth,
every infant has ceased to be an infant, and has become a child; in the
space of six years from this period, every male child will have become
a boy; add eight years to this time, and every boy will have become a
young man; in eight years more, every young man will have become an
adult man; and in the subsequent ten years, every adult man will have
acquired his highest state of physical perfection. But at what period
will this state of physical perfection decline? What is the maximum
time during which it can retain its full vigour? Is that maximum fixed?
Is there a certain number of years in which, by an inevitable law,
every adult man necessarily becomes an old man? Is precisely the same
number of years appointed for this transition to every human being?
Can no care add to that number? Can no imprudence take from it? Does
the physiological condition or the constitutional age of any two
individuals ever advance to precisely the same point in precisely the
same number of years? Physically and mentally, are not some persons
older at fifty than others are at seventy? And do not instances
occasionally occur in which an old man, who reaches even his hundredth
year, retains as great a degree of juvenility as the majority of those
who attain to eighty?

If this be so, what follows? One of the most interesting consequences
that can be presented to the human mind. The duration of the periods of
infancy, childhood, boyhood, and adolescence, is fixed by a determinate
number of years. Nothing can stay, nothing retard, the succession of
each. Alike incapable of any material protraction is the period of old
age. It follows that every year by which the term of human existence is
extended is really added to the period of mature age; the period when
the organs of the body have attained their full growth and put forth
their full strength; when the physical organization has acquired its
utmost perfection; when the senses, the feelings, the emotions, the
passions, the affections, are in the highest degree acute, intense,
and varied; when the intellectual faculties, completely unfolded
and developed, carry on their operations with the greatest vigour,
soundness, and continuity; in a word, when the individual is capable of
receiving and of communicating the largest amount of the highest kind
of enjoyment.

A consideration more full of encouragement, more animating, there
cannot be. The extension of human life, in whatever mode and degree it
may be possible to extend it, is the protraction of that portion of it,
and only of that portion of it, in which the human being is capable of
RECEIVING AND OF COMMUNICATING THE LARGEST MEASURE OF THE NOBLEST KIND
OF ENJOYMENT.

Considerations, purely physiological, establish this indubitably; but
it is curious that a class of facts, totally different from those of a
physiological nature, equally prove it; namely, the results obtained
from the observation of the actual numbers that die at different ages,
and the knowledge consequently acquired of the progressive decrement
of life. Mortality is subject to a law, the operation of which is as
regular as that of gravitation. The labours of my valued friend Mr.
Finlaison, the actuary of the National Debt, have not only determined
what that law is in relation to different nations at different periods
of their history, but this celebrated calculator has also invented a
striking mode of expressing and representing the fact. He constructed
a chart on which 100 perpendicular lines, answering to the respective
ages of human life, are laid down and numbered in succession. These
are crossed at right angles by 500 horizontal lines; so that, in the
manner of musical notation, a point may be laid down either on the
horizontal line, or on the space between any two of them: and thus,
1000 points may be laid down on each of the perpendicular lines. The
horizontal lines are in like manner numbered from 1 to 1000, ascending
from the base. Taking any observation which shows the number of living
persons that commence, and in like manner the number that die in each
particular year of human life, the calculator reduced by the rule of
three every such actual number of living persons for every separate
year to 10,000: he next showed the corresponding proportion of deaths
out of such 10,000. These proportions he represented on the chart by
a point inserted on the horizontal line or space for the number of
deaths, and on the perpendicular line for the particular age. He then
connected all the points so laid down, and the result is a curve,
representing the track of death through an equal number of human beings
existing at each age of life. As the curve rises on the perpendicular
line, at any given age, it indicates by so much an increase of the
mortality at that age; and as the curve falls, the reverse is denoted.

Now, it is a highly interesting fact, that the curves on this chart
drawn upon it before the physiological phenomena were known to the
operator, placed there because such he found to be the actual path
along which death marshals his course, exactly correspond to the epochs
which physiology teaches to be determinate stages of human existence.
The infant, the child, the boy, the adolescent, the man, the old man,
are not exposed to the same danger. The liability of each to death
is not merely different; it is widely different; the liability of
each class is uniformly the same, the circumstances influencing life
remaining the same; and under no known change of circumstances does
the relative liability of the class vary; under no change does the
liability of the adolescent become that of the infant, or the liability
of the adult that of the aged. Take from any statistical document any
number of persons; observe out of this number the proportion that
dies at the different stages just enumerated; and the period of human
life which admits of extension will be strikingly manifest. Take with
this view the Prussian statistical tables, the general correctness of
which is admitted. From these tables it appears, and the correctness
of the result is confirmed by a multitude of other tables, that out
of a million living male births, there will die in the first year of
life 180,492 infants, and out of the like number of living female
births, there will die 154,705 infants. Let us follow up the decrement
of life through the different epochs of human existence, confining
our observations to the male sex, in which the development is more
emphatically marked.

In Mr. Finlaison's report, printed by the House of Commons on the 30th
of March, 1829, there are six original observations on the mortality of
as many separate sets of annuitants of the male sex.

From an examination and comparison of these observations, it
appears—1st. That the rate of mortality falls to a minimum at
the close of the period of childhood. 2d. That from this point
the mortality rises until the termination of adolescence or the
commencement of adult age. 3d. That from the commencement of adult age
the mortality again declines, and continues to decline to the period of
perfect maturity. And 4th. That from the period of perfect maturity,
the mortality rises, and uniformly, without a single exception,
returns, at the age of forty-eight, to the point at which it stood at
the termination of adolescence. These results clearly indicate that
certain fixed periods are marked by nature as epochs of human life;
and that at the date of the recorded facts which furnish the data
for these observations, and as far as regards the class of persons
to which they relate, the age of forty-eight was the exact point at
which the meridian of life was just passed, and a new epoch began. The
following table exhibits at one view the exact results of each of the
observations. For example,

  According to The mortality   From whence  From this  And from this
      the          is at a       it rises   point it    age it again
  observation,  minimum at the   until      declines   rises, but is not
      No.           age of     the age of    to the     equal to the
                                             age of      mortality in
                                                       the 2d column
                                                       until the age of

       15   —     13      —     23    —     34   —     48

       16   —     13      —     23    —     35   —     48

       17   —     14      —     22    —     33   —     48

       18   —     13      —     23    —     33   —     48

       19   —     13      —     24    —     34   —     48

       20   —     13      —     24    —     34   —     48

The observation, No. 15, is founded on the large mass of 9,347 lives
and 4,870 deaths. From this observation, it appears that, at the age of
thirteen, the mortality out of a million is 5,742, being 174,750 less
than in the first year of infancy At the age of twenty-three, it is
15,074, being 9,332 more than at the close of childhood. At the age of
thirty-four, the period of complete manhood, it falls to 11,707, being
3,367 less than at the close of adolescence. At the age of forty-eight,
the mortality returns to 14,870, all but identically the same as at
twenty-three, the adult age. From the age of forty-eight, when, as
has been stated, life just begins to decline from its meridian, the
mortality advances slowly, but in a steady and regular progression.
Thus, at the age of fifty-eight it is 29,185, being 14,315 more than
at the preceding decade, or almost exactly double. At the age of
sixty-eight, it is 61,741, being 32,556 more than at the preceding
decade, or more than double. At the age of seventy-eight, it is
114,255, being 52,514 more than at the preceding decade. At the age of
eighty-eight, it is 246,803, being 132,548 more than at the preceding
decade.

During the first year of infancy, as has been shown, the mortality
out of a million is 180,492. At the extreme age of eighty-four, it
is 178,130, very nearly the same as in the first year of infancy.
Greatly as the mortality of all the other epochs of life is affected
by country, by station, by a multitude of influences arising out of
these and similar circumstances; yet the concurrent evidence of all
observation shows that at this and the like advanced ages the mean term
of existence is nearly the same in all countries, at all periods, and
among all classes of society. Thus, among the nobility and gentry of
England, the expectation of life at eighty-four is four years; among
the poor fishermen of Ostend, it is precisely the same. M. De Parcieux,
who wrote just ninety years ago, establishes the expectation of life
at that time in France, at the same age, to have been three and a half
years; and Halley, who wrote 120 years ago, and whose observations are
derived from documents which go back to the end of the seventeenth
century, states the expectation of life at eighty-four to be two years
and nine months.

From these statements, then, it is obvious, that from the termination
of infancy at three years of age, a decade of years brings childhood to
a close, during which the mortality, steadily decreasing, comes to its
minimum. Another decade terminates the period of adolescence, during
which the mortality as steadily advances. A third decade changes the
young adult into a perfect man, and during this period, the golden
decade of human life, the mortality again diminishes; while, during
another decade and a half, the mortality slowly rises, and returns
at the close of the period to the precise point at which it stood at
adult age. Thus the interval between the period of birth and that of
adult age includes a term of twenty-three years. The interval between
the period of adult age and that when life just begins to decline from
its meridian, includes a term of twenty-four years: consequently, a
period more than equal to all the other epochs of life from birth
to adult age is enjoyed, during which mortality makes no advance
whatever. Now the term of years included in the several epochs that
intervene between birth and adult age is rigidly fixed. Thus the
period of infancy includes precisely three years, that of childhood
ten years, and that of adolescence ten years. Within the space of time
comprehended in these intervals, physiological changes take place,
on which depend every thing that is peculiar to the epochs. These
changes cannot be anticipated, cannot be retarded, except in a very
slight degree. In all countries, among all classes, they take place in
the same order and nearly in the same space of time. In like manner,
in extreme old age, or the age of decrepitude, which may be safely
assumed to commence at the period when the mortality equals that of the
first year of infancy, namely, the age of eighty-four, physiological
changes take place, which, within a given space of time, inevitably
bring life to a close. That space of time, in all countries, in all
ranks, in all ages, or rather as far back as any records enable us to
trace the facts, appears to be the same. As within a given time the
boy must ripen into manhood, so within a given time the man of extreme
old age must be the victim of death. Consequently, it is the interval
between the adult age and the age of decrepitude, and only this, that
is capable of extension. During the interval between adult age and the
perfect meridian of life, comprehending at present, as we have seen,
a period of twenty-four years, the constitution remains stationary,
mortality making no sensible inroad upon it. But there is no known
reason why this stationary or mature period of life should, like
the determinate epochs, be limited to a fixed term of years. On the
contrary, we do in fact know that it is not fixed; for we know that the
physiological changes on which age depends are, in some cases, greatly
anticipated, and in others, proportionately postponed; so that some
persons are younger at sixty, and even at seventy, than others are at
fifty; whereas, an analogous anticipation or postponement of the other
epochs of life is never witnessed. So complete is the proof, that the
extension of human life can consist in the protraction neither of the
period of juvenility, nor in that of senility, but only in that of
maturity.

Were it necessary to adduce further evidence of this most interesting
fact, it would be found equally in the statistics of disease as
in those of mortality. Indeed, the evidence derived from both
these sources must be analogous, because mortality is invariably
proportionate to the causes of mortality, of which causes, sickness, in
all its forms, may be taken as the general or collective expression.

We do not possess the same means of illustrating the prevalence
of disease through all the epochs of life as we do of showing the
intensity of mortality; yet the report of Mr. Finlaison, already
referred to, enables us to show its comparative prevalence at several
of those stages. Thus, from this document, it appears, that among
the industrious poor of London, members of benefit societies, out
of a million of males, the proportion constantly sick at the age of
twenty-three, is 19,410; at the age of twenty-eight, it is 19,670; at
the age of thirty-three, it is 19,400; at the age of thirty-eight,
it is 23,870; at the age of forty-three, it is 26,260; at the age of
forty-eight, it is 26,140; at the age of fifty-three, it is 27,060;
at the age of fifty-eight, it is 36,980; at the age of sixty-three,
it is 57,000; at the age of sixty-eight, it is 108,040; at the age of
seventy-three and upwards, it is 317,230. The prevalence of sickness
is not an exact and invariable measure of the intensity of mortality;
but there is a close connexion between them, as is manifest from
the progressively increasing amount of sickness, as age advances.
Thus, in the first ten years from the age of twenty-three to that of
thirty-three, there is no increase of sickness, its prevalence is
all but identically the same; in the next ten years from the age of
thirty-three to that of forty-three, the increase of sickness, as
compared with that of the preceding decade, is 6,860; in the next ten
years from the age of forty-three to that of fifty-three, the increase
is only 800; in the next ten years from the age of fifty-three to
that of sixty-three, the increase is 29,940, while from the age of
sixty-three to seventy-three, it is 260,230.

Such are the results derived from the experience of disease considered
in the aggregate, all its varied forms taken together. I am enabled
further to present an exact and most instructive proof, that one
particular disease which, in this point of view, may be considered
as more important than any other, because it is the grand agent of
death, namely fever, carries on its ravages in a ratio which steadily
and uniformly increases as the age of its victim advances. Having
submitted the experience of the London Fever Hospital for the ten
years preceding January 1834, an observation including nearly 6,000
patients affected with this malady, to Mr. Finlaison, it was subjected
by him to calculation. Among other curious and instructive results to
be stated hereafter, it was found that the mortality of fever resolves
itself into the following remarkable progression. Thus suppose 100,000
patients to be attacked with this disease between the ages of 5 and
16, of these there would die - 8,266 and of an equal number

    between 15 and 26   there would die  11,494
            25 and 36      "    "    "   17,071
            35 and 46      "    "    "   21,960
            45 and 56      "    "    "   30,493
            55 and 66      "    "    "   40,708
            65 and upwards "    "    "   44,643

Thus the risk of life from this malady is twice as great at the age
of thirty-one as it is at eleven. It is also nearly twice as great
at forty-one as it is at twenty-one. It is five times as great at
sixty-one as it is at eleven, and nearly four times as great above
sixty-five as it is at twenty-one.

From the whole of the foregoing statements, it is manifest that life is
a fluctuating quantity. In order to compare this fluctuating quantity
under different circumstances, writers on this branch of statistics use
several terms, the exact meaning of which it is desirable to explain.
It is, for example, very important to have a clear understanding of
what is meant by such expressions as the following: the expectation,
the probability, the value, the decrement of life, and the law of
mortality.

1. THE EXPECTATION OF LIFE. It is important to bear in mind that
several expressions in common use have a signification perfectly
synonymous with this: namely, _share of existence_; _mean duration of
life_; _la vie moyenne_.

By these terms is expressed the total number of years, including also
the fractional parts of a year, ordinarily attained by human beings
from and after any given age. Suppose, for example, that one thousand
persons enter on the eighty-sixth year of their age: suppose the
number of years and days which each one of them lives afterwards be
observed and recorded; suppose the number ultimately attained by each
be formed into a sum total; suppose this total be divided equally among
the thousand, the quotient of this division is said to be each one's
share of existence, or his mean duration of life, or his expectation
of life. Thus, of the thousand persons in the present case supposed
to commence the age of eighty-five, suppose the number of years they
collectively attain amount to 3,500 years: the one-thousandth part of
3,500 is three and a half: three years and a half then is said to be
the expectation of life at the age of eighty-five, because, of all the
persons originally starting, this is the equal share of existence that
falls to the lot of each.

2. PROBABILITY OF LIFE; or _the probable duration of life_, _la vie
probable_. These are synonymous terms, in use chiefly among continental
writers as an expression of the comparative duration of life. The
tabular methods of setting forth the duration of life consist, for the
most part, in assuming that 10,000 infants are born; and that at the
age of one, two, three, and each successive year of life, there are
so many still remaining in existence. Fix on any age; observe what
number remain alive to commence that age; note at what age this number
decreases to one-half; the age at which they so come to one-half is
called the probable term of life; because, say the continental writers,
it is an equal wager whether a person shall or shall not be alive at
that period. Thus, suppose one thousand males commence together the age
of eighty-four; suppose the table indicate that there will be alive
at the age of eighty-five, 817; at the age of eighty-six, 648; at the
age of eighty-seven, 493; at the age of eighty-eight, 357, and so on.
In the present case, the probable duration of life at eighty-four is
said to be very nearly three years, because, at the age of eighty-seven
there are left alive 493, very nearly one-half of the thousand that
originally started together.

3. VALUE OF LIFE. This term, when used accurately, expresses the
duration of life as measured by one or other of the methods already
expounded. But it is sometimes popularly used in a loose and singularly
inaccurate sense. Thus it is very commonly said—"Such a man's life
is not worth ten years' purchase," which is the same thing as to say,
that an annuity, suppose a hundred pounds a year, payable during the
life of the person in question, is not worth ten times its magnitude,
that is one thousand pounds. If a thousand pounds be put into a bank
at some rate of interest to be agreed upon, and if a hundred pounds be
drawn every year from the stock, the expression under consideration
affirms that the person in question will be dead before the principal
and interest are exhausted. For instance, at four per cent., the value
of an annuity of one hundred pounds to a man of the age of twenty-five
is 1694_l._, which is 16-9/10 years' purchase; whereas, his expectation
of life at that age is 35-9/10 years.

4. LAW OF MORTALITY. By this term is expressed the proportion out of
any determinate number of human beings who enter on a given year of
age, that will die in that year. Every observation on the duration of
life presents certain numbers, which, by recorded facts, are found to
pass through each year of age, and also shows how many have died or
failed to pass through every year of age. Those numbers, by the rule
of three, are converted into the proportions who would die at each
age out of one million of persons, if such a number had commenced it.
Suppose, then, a million of persons to be in existence at the first
year of age; suppose a million to be in existence at the second year
of age; suppose a million to be in existence at the third year of
age; and in this manner suppose an equal number to be in existence at
the commencement of each and every year to the extreme term of human
life. Now, the proportions that by actual observation are found to
die at each and every year out of the million that were alive at the
commencement of it, form separately the law of mortality for each year,
and collectively for the whole of life.

5. DECREMENT OF LIFE. Assuming, as before, that a million of male
children are born alive (for the still-born must be excluded from
the calculation) if it be found that 180,492 would die in the first
year, it follows that the difference, namely, 819,508, will enter upon
the age of one year. Suppose the law of mortality indicate that the
proportion that will die, out of a million, between the age of one
and two, is 30,000; it is plain that the number who would die out of
819,508 will by the rule of three be 27,863, and consequently that the
residue, namely, 791,615, will remain alive, and so enter on the age
of two years. This method being pursued through each and every age to
the extreme term of life, when none of the original million survive,
the result is a table of mortality in the form in which it is commonly
presented in the works of writers on this branch of science. In the
table thus constructed there is a column containing the number of
living persons who, out of the original million, lived to enter upon
each and every year. Of this rank of numbers the difference between
each term and its next succeeding one, is the number who die in that
particular interval: that number is the measure of what is technically
called the decrement of life for that particular year, and the whole
of the decrements for each and every year taken collectively is termed
the decrement of life. The decrement of life, then, is not only not
the same as the law of mortality, but is carefully to be distinguished
from it. The law of mortality is derived from observing the number
who die out of one and the same number which is always supposed to
enter on each and every year. The decrement of life constitutes a
rank of numbers arising out of the successive deaths; that is, out of
the original million in the first year; out of the survivors of that
million in the second year; out of the survivors of those survivors in
the third year, and so on. In the first case the number of the living
is always the same; the number that die is the variable quantity: in
the second case the number of the living is the variable quantity,
while the number that die may remain pretty much the same for a
succession of years; and on casting the eye on the tables constructed
in the ordinary mode, it will be seen that the number often does remain
the same for a considerable series of years.

We have said that life is a fluctuating quantity. It fluctuates
in different countries at the same period; in the same country at
different periods; in the same country, at the same period, in
different places; in the same country, at the same period, in the
same place, among different classes; in the same country, at the same
period, in the same place, among the same class, at the different
determinate stages of life. Some few of these fluctuations, and
more especially the last, depend on the primary constitution of the
organization in which life itself has its seat, over which man has
little or no control. The greater part of them depend on external
and adventitious agencies over which man has complete control. Human
ignorance, apathy, and indolence, may render the duration of life, in
regard to large classes and entire countries, short; human knowledge,
energy and perseverance, may extend the duration of life far beyond
what is commonly imagined. It will be interesting and instructive to
select a few of the more striking examples of this from the records we
possess, few and imperfect as they are, in relation to this subject.

Of the duration of life in the earlier periods of the history of the
human race we know nothing with exactness, though there are incidental
statements which afford the means of deducing with some probability
the rate of mortality in particular situations. There has come down to
us one document through Domitius Ulpianus, a judge, who flourished in
the reign of Alexander Severus, which enables us to form a probable
conjecture at least of the opinion of the Roman people of the value
of life among the citizens of Rome in that age. It happened at Rome
as in other countries, that when an estate came into the possession
of an individual it was burthened with a provision for another person
during the life of the latter, a younger brother, for example. This
provision was called by the Romans an aliment. No estate, burthened
with such a provision, could be sold by the heir in possession, unless
the purchaser retained in his hands so much of the price as was deemed
adequate to secure the regular and continuous payment of the aliment.
This imposed upon the Romans the necessity of considering what the term
of life would probably be from and after any given age. What they did
conceive that term to be is stated in a document of Ulpianus, recorded
by Justinian, and given in the note below.[1] This document imports
that from infancy up to the age of

                      20       there should be allowed 30 years
                 From 20 to 25   "     "     "     "   28   "
                      25 to 30   "     "     "     "   25   "
                      30 to 35   "     "     "     "   22   "
                      35 to 40   "     "     "     "   20   "
                        ————
                From  50 to 55   "     "     "     "    9   "
                      55 to 60   "     "     "     "    7   "
      And at all ages above 60   "     "     "     "    5   "

But between 40 and 50, as many years were to be allowed as the age of
the party fell short of 60, deducting one year.

No clue has hitherto been obtained to the discovery of the real
meaning of this document. It is, however, highly probable that the
Romans had fallen on one of the two methods of measuring the value of
life already explained; namely, that termed the Probability of Life.
Of the two modes of determining the value of life, the probability was
more likely to occur to a Roman judge than the expectation. He had
no tables, no registers to guide him. What course, then, would he be
likely to take? Probably he would form a list of his own school-fellows
and others within his own knowledge, of the age, say, of twenty. By
prevailing on persons of his own age, on whose correctness he could
rely, to draw out similar lists, he might accumulate some thousand
names. In this list it is probable that the male sex alone would be
included, on account of the greater ease of ascertaining both their
exact age and the exact date of their death. For the same reason,
it is probable that the list would consist only of the nobility and
the inhabitants of towns. Having thus completed his list, the next
step would be to frame another list of all who died at the age of
twenty-one; and next, another list of all who died at the age of
twenty-two, and so on through each and every year of life. Now by
subtracting the number in the list, No. 1, that is, those who died
between twenty and twenty-one, from the number who originally started
at twenty, which, in other words, would be to find the decrement of
life, in the mode already explained, he would see how many lived to
commence the age of twenty-one, and so on, through each year of life.
But this would be to construct a table, showing the probable duration
of life; that is, a table from which he could observe at what advanced
age the number originally starting at twenty, and so on, came to
diminish to one-half, when it would naturally occur to him that it
is an equal wager whether such younger life would or would not be in
existence at the advanced age so ascertained. If we suppose this to
have been the method actually adopted by the Roman judge, and apply
it to the table of Ulpianus, the result obtained is consistent in an
extraordinary degree, and is highly interesting.

There is reason to believe that the mortality at present throughout
Europe, taking all countries together, including towns and villages,
and combining all classes into one aggregate, is one in thirty-six.
Süssmilch, a celebrated German writer, who flourished about the middle
of the last century, estimated it at this average at that period. The
result of all Mr. Finlaison's investigations is a conviction that the
average for the whole of Europe does not materially differ at the
present time. He has ascertained by an actual observation, that in the
year 1832 it was precisely this in the town of Ostend. Taking this
town, then, as the subject of comparison, it is found that the probable
duration of life among the male sex at Ostend exceeds the Roman
allowance by the following number of years; namely,

  At the age of 17, the excess in round
                    numbers is    5 years.
                22     "     "    5
                27     "     "    5
                32     "     "    5
                37     "     "    3
                42     "     "    3
                47     "     "    5
                52     "     "    5
                57     "     "    4
                62     "     "    4
                67     "     "    2
                72     "     "    1
                77     "     "    0

But it is not improbable that the Romans made some deduction from
what they knew to be the real value of life among the citizens of
Rome, on account of the use of the money appropriated to the aliment,
which the purchaser of the estate retained in his own hands. It has
been shown that the average mortality at present at Ostend is one
in thirty-six; which is the same thing as to assert that a new-born
child at Ostend has an expectation of thirty-five and a half years
of life. The Roman allowance from birth, _à primâ ætate_, was thirty
years. If we suppose the Romans deducted from the real value of life
five and a half years for the interest of money, it would bring the
Roman allowance and the duration of life at Ostend to the same. The
like deduction at the age of seventeen would likewise bring the
probability of life in both cases to the same. It is not likely that
the Romans, without any record of the individual facts, and acting
only on a general principle of utility, the best they could find,
would make any variation for the intermediate years of childhood and
youth: consequently the presumption is, that the duration of life at
Rome, 1300 years ago, was very much the same as it is throughout Europe
at the present day. This estimate, however, for the reasons already
assigned, includes only the resident citizens of Rome, the male sex,
and the higher classes. What the mortality was at Rome among the lower
class, including the slaves—what it was in the Roman provinces, and in
the less civilized countries of that age—we have no means of forming
even a conjecture. What it was in Europe during the succeeding ages
of barbarism we do not know. In civilized Rome, the value of life
had probably reached a very high point; in barbarian Europe we may
be sure it fell to an exceedingly low point. From that low point, in
civilized Europe, it has been slowly but gradually rising, until, in
modern times, the whole mass of the European population has, to say
the very least, reached the highest point attained by the select class
in ancient Rome. But in some favoured spots in Europe, the whole mass
has advanced considerably beyond the select class in ancient Rome. In
England, for example, the expectation of life, at the present day, for
the mass of the people, as compared with that of the mass at Ostend,
which, as has been shown, is the same as that of the whole of Europe,
is as follows:—

  At birth   41½ years.
  At 12      46¾
     17      41½
     22      38⅜
     27      35¼
     32      32
     37      28¾
     42      25½
     47      22¼
     52      19
     57      16
     62      13
     67      10½
     72       8
     77       6

It should be borne in mind that the females of the mass exceed in
duration the lives of the males at every age by two or three years.

The earliest statistical document bearing on the rate of mortality, in
any European nation, emerging from the state of barbarism, appears to
be a manuscript of the fourteenth century, relating to the mortality
of Paris, from which M. Villermé has calculated that the mortality
of Paris at that period was one in sixteen. How the individual facts
contained in this manuscript were collected, from which M. Villermé's
calculation is made, does not appear; and it makes the mortality so
excessive as to be altogether incredible. Yet a statement scarcely
less extraordinary is made with regard to Stockholm, in the middle of
the last century. From a table given by Dr. Price, vol. ii., p. 411,
it appears that, for all Sweden, between the years 1756 and 1763, the
expectation of life

  Of males at birth, was      Females,
        33¼ years.           35¾ years.

while at the same time it was at Stockholm,

  For males at birth,         Females,
        14¼ years.            18 years.

Whereas, for the twenty years preceding 1800, it was, for all Sweden,
at birth,

  Males,       Females,
   34¾.          37½.

Hitherto, in all places which man has made his abode, noxious agents
have been present which act injuriously upon his body, tending to
disturb the actions of its economy, and ultimately to extinguish life.
All these noxious agents, of whatever name or quality, may be included
under the term Causes of Mortality. Inherent in the constitution of the
body are conservative powers, the tendency of which is to resist the
influence of these causes of mortality. The actual mortality at all
times will of course be according to the relative strength of these
destructive agents, and the relative weakness of these conservative
powers. There are states of the system tending to enfeeble these
conservative powers. Such states become tests, often exceedingly
delicate, of the presence and power of the destructive agents to which
the body is exposed; and such, more especially, are, the states of
parturition, infancy, and sickness. During the prevalence of these
states, in which the conservative powers of the body are weak, life
is destroyed by causes which do not prove mortal in other conditions
of the system. Accordingly, in every age and country, the rate of
mortality among its lying-in women, its infants and its sick, may
be taken as a measure of the degree in which the state of the whole
population is favourable or unfavourable to life.

The change that has taken place in the condition of lying-in women
during the last century in all the nations of Europe cannot be
contemplated without astonishment. The mortality of lying-in women in
France, at the Hôtel Dieu of Paris, in 1780, is stated to have been
one in 15. In 1817, for the whole kingdom of Prussia, including all
ranks, it was one in 112. In England, in the year 1750, at the British
Lying-in Hospital of London, it was one in 42; in 1780, it diminished
to one in 60; in the years between 1789 and 1798, it further decreased
to one in 288; in 1822, at the Lying-in Hospital of Dublin, it was no
more than one in 223; while during the last fifteen years at Lewes, a
healthy provincial town, out of 2410 cases there have been only two
deaths, that is, one in 1205. There is no reason to suppose that the
mortality in the state of parturition is less at Lewes than in any
other equally healthy country-town in England.

Equally striking is the proof of the diminished violence of the
prevalent causes of disease and death derived from the diminished
mortality of children, the vital power of resistance being always
comparatively weak in the human infant, and consequently, the agents
that prove destructive to life exerting their main force on the new
born, and on those of tender age. From mortuary tables, preserved with
considerable accuracy at Geneva since the year 1566, it appears that at
the time of the Reformation one-half of the children born died within
the sixth year; in the seventeenth century, not till within the twelfth
year; in the eighteenth century, not until the twenty-seventh year;
consequently, in the space of about three centuries, the probability
that a child born in Geneva would arrive at maturity has increased
fivefold. In the present day, at Ostend, only half of the new-born
children attain the age of thirty; whereas, in England, they attain the
age of forty-five.

No less remarkable is the progressive diminution of mortality among
the sick of all ages. Hippocrates has left a statement, which has come
down to our times, of the history and fate of forty-two cases of acute
disease. Out of this number, thirty-seven were cases of continued
fever; of these thirty-seven febrile cases twenty-one died, above half
of the whole. The remaining five were cases of local inflammation,
and of these four were fatal; thus, of the whole number of the sick
(forty-two), twenty-five were lost. Now, even in the Fever Hospital of
London, to which, for the most part, only the worst cases that occur
in the metropolis are sent, and even of these many not until so late
a period of the disease that all hope of recovery is extinct, the
mortality ranges in different years from one in six to one in twelve;
and for a period of ten consecutive years, it is no more than one in
seven; while, in the Dublin Fever Hospital, where most of the cases are
sent very early, the average mortality from 1804 to 1812 was one in
twelve. At the Imperial Hospital at Petersburg, the average mortality
for fourteen years, ending in 1817, was one in four and a half. In the
Charité of Berlin, on an average of twenty years, from 1796 to 1817,
it was one in six. At Dresden, it was one in seven; at Munich, it was
one in nine, the lowest of any hospital of equal size in Germany. In
the year 1685, the average mortality at St. Bartholomew's and St.
Thomas's Hospitals was from one in seven to one in ten. During the ten
years from 1773 to 1783, it decreased to one in fourteen. From 1803 to
1813, it was one in sixteen. The average for fifty years from 1764 to
1813, was one in fifteen. In the smaller towns, the mortality is still
less. It is less in Edinburgh and Dublin than in London; while in the
hospital at Bath during 1827, even among the physician's patients, the
mortality was only one in twenty. In the German provincial towns, the
diminution is still more remarkable. In the hospital at Gottingen, for
example, it is only one in twenty-one.

If the accuracy of these statements could be relied on, they
would not only afford striking illustrations of the well-known fact
that extraordinary differences prevail in the rate of mortality
in different places, at different periods, and under different
circumstances; but they would further prove that, during the last
century, a steady and progressive diminution of mortality has taken
place in all the countries of Europe. But of the truth of this there
is much more certain evidence than can be derived from calculations,
the trustworthiness of the data of which is not established, and
the correctness of the calculators not known. Both the fluctuations
of mortality and the increase in the value of life in the different
countries of Europe, from the earliest period when statistical facts
began to be collected and compared, are exhibited in a striking
point of view in the following table, drawn up by Mr. Finlaison. The
facts relating to selected lives and to the mass of the people are
distinguished from each other, in order that they may be contrasted.
The data are derived from the most authentic sources, and the
calculations are made by men of the highest authority.


Let it be conceived, that at each   50  55  60  65  70  75  80  85
of the following ages, viz.        Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.Yrs.

The average duration of Human
Life of both sexes collectively
may thenceforward be assumed at
a maximum of[2]                     23  19  16  13  11   8   6   3

By how many weeks does the
average duration which results
from the most authentic Tables
at present known fall short of
the maximum Term thus assumed?

 Among the higher classes of people exclusively.

     Answer.       Name of the
                     Observer.   Wks. Wks. Wks. Wks. Wks. Wks. Wks. Wks.
In England—
Among the Government
Annuitants, between
1775 and 1822
               John Finlaison.    35    1    7   10   47   11   14   53

Among the Lives assured
at the Equitable Office,
between 1760 and 1834
                Arthur Morgan.   119   83   87   81   96   33   10   27

Among the Nominees of
the Tontine of 1693--
between that year
and 1775
               John Finlaison.   269  195  170  141  157  110   90   89

In France--
Among the Nominees of
the Tontine of 1693--
between that year and
1745           M. de Parcieux.   133   88   87   86  118   70   55   65

In Holland--
Among the Public
Annuitants, between
1615 and 1740
                M. Kersseboom.   186  118  104   75   96   61   48   84

In regard to the mass of the people.

In Breslau in Silesia,
between 1700 and 1725,
                   Dr. Halley.   275  211  181  150  166  100   36  137

In Sweden,
between 1775
and 1795,         M. Nicander,
                and Mr. Milne.   207  161  164  146  156   94   60   60

In Northampton,
in England, between
1735 and 1780,
                    Dr. Price.   209  178  145  110  125   76   65   85

In Carlisle,
in England, between
1779 and 1787,  Dr. Heysham,
                and Mr. Milne.    98   74   86   63   94   52   26   46

In all England and
Wales, between
1811 and 1831,
               John Finlaison.   100   59   65   58   87   48   37   49

In the town of Ostend,
in Flanders, between
1805 and 1832,
               John Finlaison.   276  210  184  146  143   76   50   75

In all Belgium, between
1725 and 1832,
                  M. Quetelet.   183  133  133  117  112   84   50   61


Let us trace from this table the differences that have taken place, in
different countries at different periods, in the duration of life at
a given age. Let us take the age given in the first column, namely,
fifty. Assuming, then, the highest degree of longevity hitherto
attained at the age of fifty to be twenty-three years, it appears that,
between the years 1700 and 1725, the mass of the people in Breslau,
in Silesia, fell short of reaching this period by 275 weeks; the
inhabitants of the town of Ostend in Flanders, between 1805 and 1832,
by 276 weeks; the nominees of the tontine of England, between the years
1693 and 1775, by 269 weeks; the inhabitants of the town of Northampton
in England, between 1735 and 1780, by 209 weeks; the mass of the people
in Sweden, between 1775 and 1795, by 207 weeks; the public annuitants
of Holland, between 1615 and 1740, by 186 weeks; the inhabitants of
all Belgium, between 1725 and 1832, by 183 weeks; the persons assured
at the Equitable Office, between 1760 and 1834, by 119 weeks; the
inhabitants of all England and Wales, between 1811 and 1831, by 100
weeks; the English government annuitants, between 1775 and 1832, only
by 35 weeks.

From these statements, it appears that, towards the close of the
seventeenth century, the duration of life in England was considerably
less than in France: less even than in Holland nearly a century
earlier. Thus, the nominees of the tontine of France, between the years
1693 and 1745, at the age of fifty, according to M. De Parcieux, fell
short of the maximum longevity by 133 weeks; the public annuitants of
Holland, seventy-eight years before, namely, between the years 1615 and
1740, according to M. Kersseboom, fell short of the maximum longevity
by 186 weeks; whereas, the nominees of the tontine of England, between
the years 1693 and 1775, according to Mr. Finlaison, fell short of it
by 269 weeks; a difference nearly double that of Holland, and quite
double that of France in persons of the corresponding rank in society.

Since that period, surprising changes have taken place in all the
nations of Europe; but in none has the change been so great as in
England. From that period, when its mortality exceeded that of any
great and prosperous European country, its mortality has been steadily
diminishing, and at the present time the value of life is greater in
England than in any other country in the world. Not only has the value
of life been regularly increasing until it has advanced beyond that of
any country of which there is any record; but the remarkable fact is
established, that the whole mass of its people now live considerably
longer than its higher classes did in the seventeenth and eighteenth
centuries. Thus, by inspecting the preceding table, it will be seen
that between the years 1693 and 1715, the nominees of the tontine of
England, at the age of fifty, fell short of the maximum longevity
by 269 weeks; whereas, the mass of the people in all England and
Wales, between the years 1811 and 1831, fell short of it only by 100
weeks; the entire mass having not only reached the select class, but
absolutely advanced beyond it by 169 weeks.

There cannot be a more interesting and instructive thing than to
connect these facts with their causes. This will be attempted in a
subsequent part of this work; but the reader will be incomparably
better prepared for the investigation when the processes of life have
been explained, and the influence of physical and moral agents upon
them traced. And with this exposition we now proceed.




CHAPTER V.

  Ultimate elements of which the body is composed—Proximate
  principles—Fluids and solids—Primary
  tissues—Combinations—Results—Organs, systems,
  apparatus—Form of the body—Division into head, trunk, and
  extremities—Structure and function of each—Regions—Seats
  of the more important internal organs.


1. The ultimate elements of which the human body is composed are
azote, oxygen, and hydrogen (gaseous fluids); and carbon, phosphorus,
calcium, sulphur, sodium, potassium, magnesium, and iron (solid
substances). These bodies are called elementary and ultimate, because
they are capable of being resolved by no known process into more simple
substances.

2. These elementary bodies unite with each other in different
proportions, and thus form compound substances. A certain proportion
of azote uniting with a certain proportion of oxygen, hydrogen, and
carbon, forms a compound substance possessing certain properties.
Another proportion of azote uniting with a different proportion
of oxygen, hydrogen, and carbon, forms another compound substance
possessing properties different from the former. Oxygen, hydrogen, and
carbon, uniting in still different proportions without any admixture
of azote, form a third compound possessing properties different from
either of the preceding. The compounds thus formed by the primary
combinations of the elementary substances with each other are called
PROXIMATE PRINCIPLES.

3. Each proximate principle constitutes a distinct form of animal
matter, of which the most important are named gelatin, albumen, fibrin,
oily or fatty matter, mucus, urea, pichromel, osmazome, resin, and
sugar.

4. By chemical analysis it is ascertained that all the proximate
principles of the body, however they may differ from each other in
appearance and in properties, are composed of the same ultimate
elements. Gelatin, for example, consists (in 100 parts) of azote
16-988/1000, oxygen 27-207/1000, hydrogen 7-914/1000, carbon
47-881/1000 parts. The elementary bodies uniting in the above
proportions form an animal substance, soft, tremulous, solid, soluble
in water, especially when heated, and on cooling, which may be
considered as its distinctive property, separating from its solution in
water into the same solid substance, without undergoing any change in
its chemical constitution.

5. Again, albumen consists of azote 15-705/1000, oxygen 23-872/1000,
hydrogen 7-540/1000, carbon 52-888/1000, parts. The elementary bodies
uniting in these different proportions, there results a second
proximate principle, an adhesive fluid, transparent, destitute of smell
and taste, miscible in water, but when subjected to a temperature of
about 165°, converted into a solid substance no longer capable of being
dissolved in water. This conversion of albumen from a fluid, which is
its natural state, into a solid, by the application of heat, is called
coagulation. It is a process familiar to every one. The white of egg is
nearly pure albumen, naturally a glary and adhesive fluid: by boiling,
it is coagulated into a white and firm solid.

6. In like manner, fibrin consists of azote 19-934/1000, oxygen
19-685/1000, hydrogen 7-021/1000, carbon 53-360/1000 parts, forming
a solid substance of a pale whitish colour and firm consistence, the
peculiar character of which is its disposition to arrange itself into
minute threads or fibres.

7. On the other hand, fat or oil, which is a fluid substance of a
whitish yellow colour, inodorous, nearly insipid, unctuous, insoluble
in water and burning with rapidity, consists of a larger proportion of
hydrogen, a small proportion of oxygen, and a still smaller proportion
of carbon, without any admixture of azote.

8. From this account of the composition of the proximate principles,
which it is not necessary to extend further, it is manifest that all of
them consist of the same ultimate elements, and that they derive their
different properties from the different proportions in which their
elements are combined.

9. The ultimate elements that compose the body are never found in a
separate or gaseous state, but always in combination in the form of one
or other of the proximate principles.

10. In like manner, the proximate principles never exist in a distinct
and pure state, but each is combined with one or more of the others. No
part consists wholly of pure albumen, gelatin, or mucus, but albumen is
mixed with gelatin, or both with mucus.

11. Simple or combined, every proximate principle assumes the form
either of a fluid or of a solid, and hence the most general and obvious
division of the body is into fluids and solids. But the terms fluid
and solid are relative, not positive; they merely express the fact
that some of the substances in the body are soft and liquid compared
with others which are fixed and hard; for there is no fluid, however
thin, which does not hold in solution some solid matter, and no solid,
however dense, which does not contain some fluid.

12. Fluids and solids are essentially the same in nature; they
differ merely in their mode of aggregation; hence the easy and rapid
transition from the one to the other which incessantly takes place in
the living body, in which no fluid long remains a fluid, and no solid a
solid, but the fluid is constantly passing into the solid and the solid
into the fluid.

13. The relative proportion of the fluids in the human body is always
much greater than that of the solids; hence its soft consistence and
rounded form. The excess, according to the lowest estimate, is as 6
to 1, and according to the highest, as 10 to 1. But the proportion is
never constant; it varies according to age and to the state of the
health. The younger the age, the greater the preponderance of the
fluids. The human embryo, when first perceptible, is almost wholly
fluid: solid substances are gradually but slowly superadded, and even
after birth the preponderance is strictly according to age; for in
the infant, the fluids abound more than in the child; in the child,
more than in the youth; in the youth, more than in the adolescent; in
the adolescent, more than in the adult; and in the adult, more than
in the aged. Thus, among the changes that take place in the physical
constitution of the body in the progress of life, one of the most
remarkable is the successive increase in the proportion of its solid
matter: hence the softness and roundness of the body in youth; its
hard, unequal, and angular surface in advanced life; its progressively
increasing fixedness and immobility in old age, and ultimate inevitable
death.

14. The fluids are not only more abundant than the solids, but they
are also more important, as they afford the immediate material of the
organization of the body; the media by which both its composition and
its decomposition are effected. They bear nourishment to every part,
and by them are carried out of the system its noxious and useless
matter. In the brain they lay down the soft and delicate cerebral
substance; in the bone, the hard and compact osseous matter; and the
worn-out particles of both are removed by their instrumentality. Every
part of the body is a laboratory in which complicated and transforming
changes go on every instant; the fluids are the materials on which
these changes are wrought; chemistry is the agent by which they are
effected, and life is the governing power under whose control they take
place.

15. The fluids, composed principally of water holding solid matter in
solution, or in a state of mechanical division, either contribute to
the formation of the blood, or constitute the blood, or are derived
from the blood; and after having served some special office in a
particular part of the system, are returned to the blood; and according
to the nature and proportion of the substances they contain, are
either aqueous, albuminous, mucous, gelatinous, fibrinous, oleaginous,
resinous, or saline.

16. When the analysis of the different kinds of animal matter that
enter into the composition of the body has been carried to its ultimate
point, it appears to be resolvable into two primitive forms: first, a
substance capable of coagulation, but possessing no determinate figure;
and secondly, a substance having a determinate figure and consisting of
rounded particles. The coagulable substance is capable of existing by
itself; the rounded particles are never found alone, but are invariably
combined with coagulated or coagulable matter. Alone or combined with
the rounded particles, the coagulable matter forms, when liquid, the
fluids, when coagulated, the solids.

17. When solid, the coagulable substance is disposed in one of two
forms, either in that of minute threads or fibres, or in that of minute
plates or laminæ; hence every solid of the body is said to be either
fibrous or laminated. The fibres or laminæ are variously interwoven
and interlaced, so as to form a net-work or mesh; and the interspaces
between the fibres or laminæ are commonly denominated areolæ or cells
(fig. XVII).

18. This concrete substance, fibrous or laminated, is variously
modified either alone or in combination with the rounded particles.
These different modifications and combinations constitute different
kinds of organic substance. When so distinct as obviously to possess a
peculiar structure and peculiar properties, each of these modifications
is considered as a separate form of organized matter, and is called a
PRIMARY TISSUE. Anatomists and physiologists have been at great pains
to discriminate and classify these primary tissues; for it is found
that when employed in the composition of the body, each preserves its
peculiar structure and properties wherever placed, however combined,
and to whatever purpose applied, undergoing only such modification
as its local connexions and specific uses render indispensable.
Considering every substance employed in the construction of the body,
not very obviously alike, as a distinct form of organized matter, these
primary tissues may be said to consist of five, namely, the membranous,
the cartilaginous, the osseous, the muscular, and the nervous.

19. The first primary tissue is the peculiar substance termed MEMBRANE.
It has been already stated (16) that one of the ultimate forms of
animal matter is a coagulable substance, becoming concrete or solid
under the process of coagulation. The commencement of organization
seems to be the arrangement of this concrete matter into straight
thready lines, at first so small as to be imperceptible to the naked
eye. Vast numbers of these threads successively uniting, at length
form a single thread of sufficient magnitude to be visible, but still
smaller than the finest thread of the silkworm. If the length of these
threads be greater than their breadth, they are called fibres; if,
on the contrary, their breadth exceed their length, they are termed
plates or laminæ. By the approximation of these fibres or plates in
every possible direction, and by their accumulation, combination, and
condensation, is constituted the simplest form of organized substance,
the primary tissue called membrane.

20. Membrane once formed is extensively employed in the composition
of the body: it is indeed the material principally used in producing,
covering, containing, protecting, and fixing every other component
part of it. It forms the main bulk of the cartilaginous tissue; it
receives into its cells the earthy matter on which depend the strength
and hardness of the osseous tissue; it composes the canals or sheaths
in which are deposited the delicate substance of the muscular, and the
still more tender pulp of the nervous tissue; it gives an external
covering to the entire body; it lines all its internal surfaces; it
envelopes all internal organs; it enters largely as a component element
into the substance of every organ of every kind; it almost wholly
constitutes all the internal pouches and sacs, such as the stomach, the
intestines, the bladder; and all tubes and vessels, such as arteries,
veins, and lymphatics; it furnishes the common substance in which
all the parts of the body are, as it were, packed; it fills up the
interstices between them; it fixes them in their several situations; it
connects them all together; in a word, it forms the basis upon which
the other parts are superinduced; or rather the mould into which their
particles are deposited; so that were it possible to remove every other
kind of matter, and to leave this primary tissue unaltered in figure
and undiminished in bulk, the general form and outline of the body, as
well as the form and outline of all its individual parts, would remain
unchanged.

21. The properties which belong to membrane are cohesion, flexibility,
extensibility, and elasticity. By its property of cohesion, the several
parts of the body are held together; by its combined properties of
cohesion, flexibility, and extensibility, the body in general is
rendered strong, light, and yielding, while particular parts of it
are made capable of free motion. But elasticity, that property by
which parts removed from their situation in the necessary actions of
life are restored to their natural position, may be regarded as its
specific property. The varied purposes accomplished in the economy
by the property of elasticity will be apparent as we advance in our
subject. Meantime, it will suffice to observe that it is indispensable
to the action of the artery in the function of the circulation; to the
action of the thorax in the function of respiration; to the action of
the joints in the function of locomotion: in a word, to the working
of the entire mechanism by which motion of every kind and degree
is effected. All these properties are physical, not vital; vital
properties do belong even to this primary form of animal matter; but
they are comparatively obscure. In the tissue with which organization
commences, and which is the least removed from an inorganic substance,
the properties that are prominent and essential are merely physical.

22. By chemical analysis, membrane is found to contain but a small
proportion of azote, the peculiar element of animal matter. Its
proximate principles are gelatin, albumen, and mucus. In infancy and
youth, gelatin is the most abundant ingredient; at a more advanced
period, albumen predominates[3]. Gelatin differs from albumen in
containing a less proportion of azote and a greater proportion of
oxygen; on both accounts it must be regarded as less animalized. Thus
animalization bears a certain relation to organization. The simplest
animal tissue is the least animalized, and the least of all at the
earliest period of life. Not only are the physical and mental powers
less developed in the young than in the adult, but the very chemical
composition of the primary tissue of which the body is constructed is
less characteristic of the perfect animal.

23. Membrane exists under several distinct forms; a knowledge of the
peculiarities of which will materially assist us in understanding the
composition of the body. The simplest form of membrane, and that which
is conceived to constitute the original structure from which all the
others art produced, is termed the _cellular_. When in thin slices,
_cellular membrane_ appears as a semi-transparent and colourless
substance; when examined in thicker masses, it is of a whitish or
greyish colour. It consists of minute threads, which cross each other
in every possible direction, leaving spaces between them, and thus
forming a mesh or net-work (fig. XVII.), not unlike the spider's web.
The term cells, given to these interspaces, is employed rather in a
figurative sense than as the expression of the fact; for there are no
such distinct partitions as the term cell implies. The best conception
that can be formed of the arrangement of the component parts of
this structure is, to suppose a substance consisting of an infinite
number of slender thready lines crossing each other in every possible
direction (fig. XVII.). The interspaces between these lines during
life, and in the state of health, are filled with a thin exhalation of
an aqueous nature, a vapour rather than a fluid, rendering and keeping
the tissue always moist. This vapour consists of the thinner part of
the blood, poured into these interstitial spaces by a process hereafter
to be described, termed secretion. When occupying those spaces, it
makes no long abode within them, but is speedily removed by the process
of absorption. In health, these two operations exactly equal each
other; but if any cause arise to disturb the equilibrium, the vapour
accumulates, condenses and forms an aqueous fluid, which distends the
cells and gravitates to the most depending parts. Slightly organized
as this tissue is, and indistinct as its vita functions may be, it
is obvious that it must be the seat of at least two vital functions,
secretion and absorption.

[Illustration: Fig. XVII.

A single film of the cellular tissue lifted up and slightly distended.]

24. It is certain that the interspaces or cells of this membrane have
no determinate form or size, that they communicate freely with each
other, and that this communication extends over the whole body; for if
a limb which has been infiltrated be frozen, a thousand small icicles
will be formed, assuming the shape of the containing cells, some of
which are found to be circular and others cylindrical, and so on. If
air or water escape into any particular part of the body, it is often
effused over the whole extent of it, and butchers are observed to
inflate animals by making a puncture in some part where the cellular
tissue is loose, and from this one aperture the air is forced to the
most distant parts of the body.

25. Cellular membrane, variously modified and disposed, forms the
main bulk of all the other solid parts of the body, constituting
their common envelope and bond of union, and filling up all their
interstices. It is dense or loose, coarse or fine, according to its
situation and office. Wherever it is subject to pressure, it is dense
and firm, as in the palm of the hand and the sole of the foot; around
the internal organs it is more loose and delicate, and it becomes finer
and finer as it divides and subdivides, in order to envelope the soft
and tender structures of the body.

[Illustration: Fig. XVIII.

A portion of cellular tissue, very highly magnified, showing the
strings of globules of which its ultimate fibres are by some supposed
to consist.]

26. According to some who have carefully examined with the microscope
its component threads, they consist of minute particles of a globular
figure (fig. XVIII.); other microscopical observers regard the cellular
threads as coagulated or condensed animal substance, perfectly
amorphous (without form).

27. Every part of this tissue is penetrated by arteries, veins,
absorbents, and nerves, endowing it with properties truly vital, though
in a less degree than any of the other primary tissues; and varied and
important as the uses are which it serves in the economy, the most
manifest, though certainly not the only ones, are those which depend
upon its physical properties of cohesion, flexibility, extensibility,
and elasticity.

[Illustration: Fig. XIX. 1, A portion of adipose tissue; 2, minute bags
containing the fat; 3, a cluster of the bags, separated and suspended.]

28. The tissue which contains the fat, termed the _adipose_, is
the second form of membrane; it is obviously a modification of the
cellular, from which it differs both in the magnitude of its fibres,
whence it constitutes a tougher and coarser web, and in their
arrangement; for it is so disposed as to form distinct bags in which
the fat is contained. Adipose tissue consists of rounded packets,
separated from each other by furrows (fig. XIX. 2, 2); each packet
is composed of small spheroidal particles (fig. XIX. 2, 2); each
particle is again divisible into still smaller grains, which, on minute
inspection, present the appearance of vesicles filled with the adipose
matter (fig. XIX. 3).

29. The cells of the cellular tissue, as has been shown (24), are
continuous over the whole body; but each adipose vesicle is a distinct
bag, having no communication whatever with any other (fig. XIX. 2, 2).
The cellular tissue is universally diffused; but the adipose is placed
only in particular parts of the body; principally beneath the skin, and
more especially between the skin and the abdominal muscles, and around
some of the organs contained in the chest and abdomen, as the heart,
the kidneys, the mesentery, and the omenta. In most of these situations
some portion of it is generally found, whatever be the degree of
leanness to which the body may be reduced; while in the cranium, the
brain, the eye, the ear, the nose, and several other organs, there is
none, whatever be the degree of corpulency. The uses of the fat, which
are various, will be stated hereafter.

30. The third form of membrane is termed the

_serous_. Like the adipose, _serous membrane_ is a modification of
the cellular, and, like it also, it is limited in its situation to
particular parts of the body, that is, to its three great cavities,
namely, the head, the chest, and the abdomen. To the two latter it
affords an internal lining, and to all the organs contained in all
the three cavities, it affords a covering. By its external surface it
is united to the wall of the cavity or the substance of the organ it
invests; by its internal surface it is free and unattached; whence this
surface is in contact only with itself, forming a close cavity or shut
sac, having no communication with the external air. Smooth and polished
(fig. XX.), it is rendered moist by a fluid which is supposed to be
exhaled in a gaseous state from the serum of the blood; and from this
serous fluid the membrane derives its name.

[Illustration: Fig. XX.

A portion of intestine, showing its external surface or serous coat.]

31. Though thin, serous membrane is dense, compact, and of great
strength in proportion to its bulk: it is extensible and elastic;
extensible, for it expands with the dilatation of the chest in
inspiration; elastic, for it contracts with the diminished size
of the chest in expiration. In like manner, it stretches with the
enlargement of the stomach during a hearty meal, and contracts as
the stomach gradually diminishes on emptying itself of its contents.
It is furnished with no blood-vessels large enough to admit the
colouring matter of the blood; but it is supplied with a great number
of the colourless vessels termed exhalents, with the vessels termed
absorbents, and with a few nerves. It indicates no vital properties,
but those which are common to the simple form of the primary tissue.
Its specific uses are to afford a lining to the internal cavities; to
furnish a covering to the internal organs; by its polished and smooth
surface, to allow a free motion of those organs on each other, and by
the moisture with which it is lubricated, to prevent them from adhering
together, however closely, or for however long a period they may be in
contact.

32. The fourth form of membrane, the _fibrous_, named from the obvious
arrangement of its component parts, consists of longitudinal fibres,
large enough to be visible to the naked eye, placed parallel to each
other, and closely united. Sometimes these fibres are combined in such
a manner as to form a continuous and extended surface, constituting
a thin, smooth, dense, and strong membrane, such as that which lines
the external surface of bones termed PERIOSTEUM, or the internal
surface of the skull (dura mater). At other times, they form a firm and
tough expansion (aponeurosis) which descends between certain muscles,
separating them from each other, and affording a fixed point for the
origin or insertion of neighbouring muscles; or which is stretched
over muscles, and sometimes over even an entire limb, in order to
confine the muscles firmly in their situation, and to aid and direct
their action (fig. XXVII.). Fibrous membrane also constitutes the
compact, strong, tough, and flexible bands used for tying parts firmly
together, termed LIGAMENTS, principally employed in connecting the
bones with each other, and particularly about the joints; and lastly,
fibrous membrane forms the rounded white cords in which muscles often
terminate, called TENDONS (fig. XXV., XXVI.), the principal use of
which is to connect the muscles with the bones, and to serve as cords
or ropes to transmit the action of the muscle to a distant point, in
the accomplishment of which purposes their operation appears to be
entirely mechanical.

33. The fifth form of membrane, the _mucous_ (fig. XXI.), derives its
name from the peculiar fluid with which its surface is covered, called
mucus, and which is secreted by numerous minute glands, imbedded in
the substance of the membrane. As serous membrane forms a shut sac,
completely excluding the air, mucous membrane, on the contrary, lines
the various cavities which are exposed to the air, such as the mouth,
the nostrils, the wind-pipe, the gullet, the stomach, the intestines,
the urinary organs, and the uterine system. Its internal surface, or
that by which it is attached to the passages it lines, is smooth and
dense; its external surface, or that which is exposed to the contact
of the air, is soft and pulpy, like the pile of velvet (fig. XXI.). It
bears a considerable resemblance to the external surface of the rind of
the ripe peach.

[Illustration: Fig. XXI.

A portion of the stomach, showing its internal surface or mucous coat.]

Unlike all the other tissues of this class, the mucous membranes are
the immediate seat of some of the most important functions of the
economy; in the lung, of respiration; in the stomach, of digestion; in
one part of the intestine, of chylification; in another, of excretion;
while in the mouth and nose, they are the seat of the animal functions
of taste and smell; and they are highly organized in accordance with
the importance of the functions they perform.

34. The last form of membrane which it is necessary to our present
purpose to particularize, is that which constitutes the external
covering of the body, and which is called the _skin_. The skin is
everywhere directly continuous with the mucous membranes that line the
internal passages, and its structure is perfectly analogous. Both the
external and the internal surface of the body may be said therefore to
be covered by a continuous membrane, possessing essentially the same
organization, and almost identically the same chemical composition.
The skin is an organ which performs exceedingly varied and important
functions in the economy, to the understanding of which it is necessary
to have a clear conception of its structure; some further account of it
will therefore be required; but this will be more advantageously given
when the offices it serves are explained.

[Illustration: Fig. XXII. Portions of cartilage, seen in section.]

35. Such is the structure, and such are the properties, of the
first distinct form of organized matter. The second primary tissue,
termed the CARTILAGINOUS (fig. XXII.), is a substance intermediate
between membrane and bone. The nature of its organization is not
clearly ascertained. By some anatomists, it is regarded as a uniform
and homogeneous substance, like firm jelly, without fibres, plates,
or cells; others state that they have been able to detect in it
longitudinal fibres, interlaced by other fibres in an oblique and
transverse direction, but without determinate order. All are agreed
that it is without visible vessels or nerves: not that it is supposed
to be destitute of them, but that they are so minute as to elude
observation. Its manifest properties are wholly mechanical. It is
dense, strong, inextensible, flexible, and highly elastic. It is
chiefly by its property of elasticity that it accomplishes the various
purposes it serves in the economy. It is placed at the extremities of
bones, especially about the joints, where, by its smooth surface, it
facilitates motion, and, by its yielding nature, prevents the shock or
jar which would be produced were the same kind and degree of motion
effected by a rigid and inflexible substance. Where a certain degree
of strength with a considerable degree of flexibility are required, it
supplies the place of bone, as in the spinal column, the ribs and the
larynx.

[Illustration: Fig. XXIII.

Membranous portion of bone; the osseous portion being so completely
removed, that the bone is capable of being tied in a knot.]

36. The third distinct form of organized matter is termed the
OSSEOUS tissue. Bone is composed of two distinct substances, an animal
and an earthy matter: the former organic, the latter inorganic. The
animal or organic matter is analogous both in its nature and in its
arrangement to cellular tissue; the earthy or inorganic matter consists
of phosphoric acid combined with lime, forming phosphate of lime. The
cellular tissue is aggregated into plates or laminæ, which are placed
one upon another, leaving between them interspaces or cells, in which
is deposited the earthy matter (phosphate of lime). If a bone, for
example, the bone called the radius, one of the bones of the fore-arm,
be immersed in diluted sulphuric, nitric, muriatic, or acetic acid, it
retains its original bulk and shape; it loses, however, a considerable
portion of its weight, while it becomes so soft and pliable, that it
may be tied in a knot (fig. XXIII.). In this case, its earthy matter
is removed by the agency of the acid, and is held in solution in the
fluid; what remains is membranous matter (cellular tissue). If the
same bone be placed in a charcoal fire, and the heat be gradually
raised to whiteness, it appears on cooling as white as chalk; it is
extremely brittle; it has lost much of its weight, yet its bulk and
shape continue but little changed. In this case, the membraneous matter
is wholly consumed by the fire, while the earth is left unchanged (fig.
XXIV.). Every constituent atom of bone consists, then, essentially
of animal and earthy matter intimately combined. A little more than
one-third part consists of animal matter (albumen), the remaining
two-thirds consist of earthy matter (phosphate of lime); other saline
substances, as the fluate of lime and the phosphate of magnesia, are
also found in minute quantity, but they are not peculiar to bone.

[Illustration: Fig. XXIV.

Earthy portion of bone.]

37. In general, the osseous tissue is placed in the interior of the
body. Even when bone approaches the surface, it is always covered
by soft parts. It is supplied with but few blood-vessels, with
still fewer nerves, with no absorbents large enough to be visible,
so that though it be truly alive, yet its vital properties are not
greatly developed. The arrangement of its component particles is
highly curious; the structure, the disposition, and the connexion of
individual bones afford striking examples of mechanism, and accomplish
most important uses in the economy; but those uses are dependent
rather upon mechanical than vital properties. The chief uses of bone
are— 1. By its hardness and firmness to afford a support to the soft
parts, forming pillars to which the more delicate and flexible organs
are attached and kept in their relative positions. 2. To defend the
soft and tender organs by forming a case in which they are lodged and
protected, as that formed by the bones of the cranium for the lodgment
and protection of the brain (fig. XLVII.); by the bones of the spinal
column for the lodgment and protection of the spinal cord (fig.
XLVIII.); by the bones of the thorax (fig. LIX.), for the lodgment and
protection of the lungs, the heart, and the great vessels connected
with it (fig. LIX.). 3. By affording fixed points for the action of the
muscles, and by assisting in the formation of joints to aid the muscles
in accomplishing the function of locomotion.

38. All the primary tissues which have now been considered consist of
precisely the same proximate principles. Albumen is the basis of them
all; with the albumen is always mixed more or less gelatin, together
with a minute quantity of saline substance: to the osseous tissue is
superadded a large proportion of earthy matter. With the exception
of the mucous, the organization of all these tissues is simple;
their vital properties are low in kind and in degree; their decided
properties are physical, and the uses they serve in the economy are
almost wholly mechanical.

[Illustration: Fig. XXV.

Portion of a muscle; showing (_a_) the muscular fibres and their
parallel direction; and (_b_) the termination of the fibres in tendon.]

39. But we next come to a tissue widely different in every one of
those circumstances, a tissue consisting of a new kind of animal
matter, and endowed with a property not only peculiar to itself,
but proper to living substance, and characteristic of a high degree
of vital power. MUSCULAR TISSUE, the fourth distinct form of animal
matter, commonly known under the name of flesh, is a substance
resembling no other in nature. It consists of a soft and pulpy
substance, having little cohesive power, arranged into fibres which
are distinctly visible to the naked eye, and which are disposed in a
regular and uniform manner, being placed close and parallel to each
other (fig. XXV.). These fibres are every where pretty uniformly the
same in shape, size, and general appearance, being delicate, soft,
flattened, and though consisting only of a tender pulp, still solid
(fig. XXV.). When examined under the microscope, fibres, which to the
naked eye appear to be single threads, are seen to divide successively
into smaller threads, the minutest or the ultimate division not
exceeding, as is supposed, the 40,000th part of an inch in diameter. On
the other hand, the fibres which are large enough to be visible to the
naked eye, are obviously aggregated into bundles of different magnitude
in different muscles, but always of the same uniform size in the same
muscle (fig. XXV.).

[Illustration: Fig. XXVI.

Two portions of muscle; one of which, _a_, is covered with membrane;
the other, _b_, is uncovered; _c_, the muscular fibres terminating in
tendon.]

40. The ultimate thread, or the minutest division of which the
muscular fibre is susceptible, is called a filament; the smallest
thread which can be distinguished by the naked eye is termed a fibre
(fig. XXVI.); and the bundle which is formed by the union of fibres
is denominated a fasciculus. The proper muscular substance is thus
arranged into three distinct forms progressively increasing in
size,—the filament, the fibre, and the fasciculus. The filament, the
fibre, the fasciculus, as well as the muscle itself, formed by the
aggregation of fasciculi, is each inclosed in its own distinct sheath
of cellular membrane (fig. XXVI. _a_).

[Illustration: Fig. XXVII.

Portion of a muscle enclosed in a sheath of fascia or aponeurosis.]

41. The composition of the ultimate filament has been very carefully
examined by many distinguished physiologists with microscopes of high
magnifying power. Under some of these microscopes the filament appears
to consist of a series of rounded particles or globules of the same
size as the particles of the blood when deprived of their colouring
matter, so that it looks like a string of pearls (fig. XXVIII.), each
globule being commonly stated to be about the 2000th part of an inch
in diameter. But it is now pretty generally agreed that this globular
appearance of the ultimate muscular fibre vanishes under the more
improved microscopes of the present day, and, as viewed by the latter,
appears as a peculiar pulpy substance arranged into threads of extreme
minuteness, placed close and parallel to each other, intersected by a
great number of delicate lines passing transversely across the muscular
threads (fig. XXIX.),

[Illustration: Fig. XXVIII.

Ultimate fibres of muscle, very greatly magnified; showing the strings
of globules of which they are supposed by some to consist.]

42. With the exception of the organs of sense, the muscular tissue is
more abundantly supplied with arteries, veins, and nerves, than any
other substance of the body. Every ultimate thread or filament appears
to be provided with the ultimate branch of an artery, vein, and nerve.
These vessels are seen ramifying on the surface of the delicate web of
membrane that incloses the pulp, but cannot be traced into it.

[Illustration: Fig. XXIX.

The appearance of the ultimate muscular fibres and of their transverse
lines, as seen under the microscope of Mr. Lister, when the object is
magnified 500 diameters.]

43. The proximate principle of which the muscular pulp is composed
is fibrin. From the pulp, when inclosed in its sheath of membrane,
albumen, jelly, various salts, and a peculiar animal extract called
osmazome, are also obtained; but these substances are probably derived
from the membranous, not the muscular, matter. Fibrin contains a larger
proportion of azote, the element peculiar to the animal body, and by
the possession of which its chemical composition is distinguished from
that of the vegetable, than any other animal substance.

[Illustration: Fig. XXX.

Portion of the trunk of a nerve; dividing into branches.]

44. Muscular tissue possesses a slight degree of cohesion, a high
degree of flexibility and extensibility, but no degree of elasticity;
for although muscle, considered as a compound of muscular substance and
membrane, be highly elastic, yet this property is probably altogether
owing to the membranous matter in which it is enveloped. Its peculiar
and distinctive property is vital, not physical, and consists in the
power of diminishing its length, or of contracting or shortening itself
on the application of a stimulus. This property, which is termed
contractility, is the great, if not the sole source of motion in the
body. Without doubt, elasticity and gravity, under the generating and
controlling powder of contractility, aid in accomplishing various
kinds of motion. Thus membranes, tendons, ligaments, cartilages, and
bones, by their physical and mechanical properties, modify, economize,
facilitate, concentrate and direct the motive power generated by the
pure muscular substance; but still the only real source of motion in
the body is muscular tissue, and the only mode in which motion is
generated is by contractility. This will be more fully understood
hereafter.

[Illustration: Fig. XXXI.

Ultimate fibres of nerve, very highly magnified; showing the strings of
globules of which they consist.]

45. The last primary tissue, termed the NERVOUS, is equally distinct
in nature and peculiar in property. It consists of a soft and pulpy
matter, of a brownish white colour (fig. XXX.). According to some,
the nervous, like the muscular pulp, is composed of minute globules,
arranged in the same manner like a string of pearls (fig. XXXI.);
according to others, it consists of solid elongated threads, of a
cylindrical form, differing in thickness from that of a hair to the
finest fibre of silk. The pulp, whatever its form of aggregation, is
inclosed in a sheath of delicate cellular tissue. This external or
containing membrane is called the neurilema, or the nerve-coat; the
internal or contained substance, the proper nervous matter, is termed
the nerve-string. The nerve-string, enveloped in its nerve-coat,
constitutes the nervous filament. As in the muscle, so in the nerve,
many filaments unite to form a fibre, many fibres to form a fasciculus,
and many fasciculi to form the large cord termed a nerve. Moreover,
as in the muscle, so in the nerve, the filament, the fibre, the
fasciculus, the nervous cord itself, are each enveloped in its own
distinct sheath of cellular membrane; but the arrangement of the
nervous fibres differs from that of the muscular in this, that though
the nervous fibres are placed in juxtaposition, yet they do not,
like the muscular, maintain through their entire course a parallel
disposition, but cross and penetrate each other, so as to form an
intimate interlacement (fig. XXXII.).

[Illustration: Fig. XXXII.

Nervous fibres, deprived of their neurilema and unravelled, showing the
smaller threads, or filaments, of which the fibres consist.]

46. The nervous pulp is at least as liberally supplied with
blood-vessels as the muscular; the vessels are spread out upon the
nerve-coat, in which they divide into innumerable branches of extreme
minuteness, the distribution of which is so perfect, that there is
not a particle of nervous matter which is not supplied both with an
arterial and a venous vessel. Hence the neurilema is not merely a
sheath containing and protecting the nervous pulp, but it affords an
extended mechanical surface for sustaining the arterial vessels, from
which the pulp is probably secreted, and certainly nourished.

47. Albumen, in conjunction with a peculiar fatty matter, constitutes
the chief proximate principles of which the nervous tissue is composed.
To these are added a small proportion of the animal substance termed
osmazome, a minute quantity of phosphorus, some salts, and a very large
proportion of water; for out of one hundred parts of nervous substance,
water constitutes as much as eighty. Its peculiar vital property is
sensibility; and as all motion depends on the contractility of the
muscular fibre, so all sensation depends on the sensibility of the
nervous substance.

48. Such are the primary tissues, or the several kinds of organized
matter of which the body is composed; and from this account it is
obvious that they consist of three only—namely, the concrete matter
forming the basis of membrane, the pulpy matter forming the proper
muscular substance, and the pulpy matter forming the proper nervous
substance. Of these three kinds of animal matter the component parts of
the body consist. In combining to form the different structures, these
primary substances are intermixed and arranged in a great variety of
modes; and from these combinations and arrangements result either an
organ, a system, or an apparatus.

49. As filaments unite to form fibres, and fibres to form tissues, so
tissues unite to form organs: that is, bodies having a determinate
size and figure, and capable of performing specific actions. The
cellular, the muscular, and the nervous tissues are not organs;
membranes, muscles, and nerves are organs. The tissue, the simple
animal substance, is merely one of the elements of which the organ
is composed; the organ is compounded of several of those simple
substances, arranged in a determinate manner, and moulded into a given
shape, and so constituting a specific instrument. The basis of the
muscle is muscular tissue; but to this are added, invariably, membrane,
often tendon, and always vessels and nerves. It is this combination
that forms the specific instrument called a muscle, and that renders it
capable of performing its specific action. And every such combination,
with its appropriate endowment, constitutes an organ.

50. Organs are arranged into groups or classes, according as they
possess an analogous structure, and perform an analogous function; and
this assemblage constitutes a SYSTEM. All the muscles of the body,
for example, whatever their size, form, situation, or use, have an
analogous structure, and perform an analogous function, and hence are
classed together under the name of the muscular system. All the bones,
whatever their figure, magnitude, density, position, or office, are
analogous in structure and function; and hence are classed together
under the name of the osseous system. For the same reason, all the
cartilages, ligaments, vessels and nerves, form respectively the
cartilaginous, ligamentous, vascular and nervous systems.

51. An APPARATUS, on the contrary, is an assemblage of organs, it
may be differing widely from each other in structure, and exercising
various and even opposite functions; but all nevertheless concurring
in the production of some common object. The apparatus of nutrition
consists of the organs of mastication, deglutition, digestion,
absorption, and assimilation. Among the individual organs which concur
in carrying on these functions may be reckoned the lips, the teeth,
the tongue, the muscles connected with the jaws, the gullet, the
stomach, the duodenum, the small intestines, the pancreas, the liver,
the lacteal vessels, the mesenteric glands, and the lungs. Many of
these organs have no similarity in structure, and few have any thing
analogous in function; yet all concur, each in its appropriate mode and
measure, to the conversion of the aliment into blood. In the apparatus
of respiration, in that of circulation, of secretion, of excretion;
in the apparatus of locomotion, in the apparatus of sensation, and
more especially in the apparatus of the specific sensations,—vision,
hearing, smell, taste, touch, organs are combined which have nothing
in common but their concurrence in the production of a common end:
but this concurrence is the principle of their combination; and the
individual organs having this conjoint operation, taken together,
constitute an apparatus.

52. A clear idea may now be affixed to the terms structure and
organization. Structure may be considered as synonymous with
arrangement; the disposition of parts in a determinate order; that
which is constructed or built up in a definite mode, according to a
determinate plan. The arrangement of the threads of the cellular web
into areolæ or cells; the combination of the primary threads into
fibres or laminæ; the disposition of the muscular pulp into filaments,
placed parallel to each other; the investment of the filaments in
membraneous sheaths; the combination of the filaments, included in
their sheaths, into fibres; the aggregation of fibres into fasciculi;
and the analogous arrangement and combination of the nervous pulp,
are examples of structure. But when those structures are applied to
particular uses; when they are so combined and disposed as to form
a peculiar instrument, endowed with a specific function; when the
cellular fibres, for example, are so arranged as to make a thin, dense,
and expanded tissue; when to this tissue are added blood-vessels,
absorbents, and nerves; when, in a word, a membrane is constructed,
an organ is formed; when, in like manner, to the muscular and the
nervous fibres, arranged and moulded in the requisite mode, are added
blood-vessels, absorbents, and nerves, other organs are constructed
capable of performing specific functions: and this is organization—the
building up of organs—the combination of definite structures
into special instruments. Structure is the preparatory process of
organization; the one is the mere arrangement of the material; the
other is the appropriation of the prepared material to a specific use.

53. The term organization is employed in reference both to the
component parts of the body, and to the body considered as a whole. We
speak of an organized substance and of an organized body. An organized
substance is one in which there is not only a definite arrangement
of its component parts (structure), but in which the particular
arrangement is such as to fit it for accomplishing some special
use. Every organized substance is therefore essentially a special
organ; limited in its object it may be, and perhaps only conducive
to some further object; but still its distinctive character is, that
it has a peculiar structure, fitting it for the accomplishment of
some appropriate purpose. On the other hand, an organized body is a
congeries of organs—the aggregate of the individual organs. Attention
was directed in the early part of this work to one peculiar and
essential character, by which such an organized is distinguished from
an unorganized body. Between the individual parts of the organized body
there is so close a relation, that no one of them can be removed or
injured, or in any manner affected without a corresponding affection of
the whole. The action of the heart cannot cease without the cessation
of the action of the lung; nor that of the lung without that of the
brain; nor that of the brain without that of the stomach; in a word,
there is no organ in whatever distant nook of the system it be placed,
or however apparently insignificant its function, that is not necessary
to the perfection of the whole. But into whatever number of portions an
unorganized body may be divided, each portion retains the properties of
the mass, and constitutes in itself a perfect existence; there being
no relation between its individual parts, excepting that of physical
attraction: on the contrary, each component part of an organized body,
being endowed with some appropriate and specific power, on the exercise
of which the powers of all the other parts are more or less dependent,
the whole must necessarily suffer if but one part fail.

54. From the whole, then, we see that the human body is a congeries of
organs; that those organs are constructed of a few simple tissues; and
that all its parts, numerous, diversified, and complex as they are, are
composed of but three primary forms of animal matter variously modified
and combined.

[Illustration: Fig. XXXIII.

Muscles of the back and shoulders; showing their symmetrical
disposition.]

55. But though by the analysis of its component parts, this machine,
so complex in its construction, and so wonderfully endowed, may be
reduced to this state of simplicity; and although this analytical view
of it be highly useful in enabling us to form a clear conception of the
nature of its composition; yet it is only by considering its individual
parts such as they actually are, and by studying their situation,
connexion, structure, and action, that we can understand it as a whole,
and apply our knowledge of it to any practical use.

56. Viewing then the human body as a complicated whole, as a congeries
of organs made up of various combinations of simple tissues, it may
be observed, in reference to its external configuration, that it is
rounded. This rounded form is principally owing to the large proportion
of fluids which enter into its composition. The roundness of the face,
limbs, and entire surface of the child, are in striking contrast to
the unequal and irregular surface of the old man, whose humours are
comparatively very much smaller in quantity.

57. The length of the human body exceeds its breadth and thickness;
the degree of the excess varying at different periods of life, and
according to the peculiar constitution of the individual. In the
extremities, the bones, muscles, vessels, and nerves, are especially
distinguished by their length.

[Illustration: Fig. XXXIV.

Front view of the skeleton. 1. the head; 2. the trunk; 3. the superior
extremities; 4. the inferior extremities.]

[Illustration: Fig. XXXV.

Back view of the skeleton. 1. the head; 2. the trunk; 3. the superior
extremities; 4. the inferior extremities.]

58. The form of the human body is symmetrical, that is, it is
capable of being divided into two lateral and corresponding halves.
Suppose a median line to pass from the vertex of the head through the
centre of the spinal column (fig. XXXIV. 1, 2); if the body be well
formed, it will be divided by this line into two exactly equal and
corresponding portions (fig. XXXV. 1). This symmetrical disposition
of the body is not confined to its external configuration. It is
true of many of the internal organs; but principally, as has been
already stated, of those that belong to the animal life. The brain and
the spinal cord are divisible into two exactly equal halves (figs.
XLVIII. _d_, and XLIX. 1, 2, 3); the organs of sense are double and
symmetrical: the muscles of one side of the body exactly correspond to
those of the other (fig. XXXIII.); the two hands and arms and the two
lower extremities are alike (figs. XXXIV., XXXV.); but for the most
part, the organs of the organic life, the stomach, the intestines, the
liver, the spleen, for example, are single, and not symmetrical.

59. The human body is divided into three great portions, the head, the
trunk, and the extremities (figs. XXXIV. and XXXV. 1, 2, 3, 4).

60. By the HEAD is meant all that part of the body which is placed
above the first bone of the neck (fig. XXXIV. 1). It is of a spheroidal
figure, broader and deeper behind than before, somewhat like an egg in
shape, with the broad end behind; it is flattened at its sides (figs.
XXXV. 1, and XXXVI. 2, 4). Its peculiar figure renders it at once
stronger and more capacious than it could have been had it possessed
any other form. It is supported by its base on the spinal column, to
which it is attached by the peculiar structure termed a joint (fig.
XXXIV.), and fastened by ligaments of exceeding strength.

61. The head contains the central organ of the nervous system; the
organs of the senses, with the exception of that of touch; and the
organs of mastication. It comprehends the cranium and the face. Both
are composed partly of soft parts, as the teguments, namely, skin, fat,
&c., and muscles; and partly of bones.

[Illustration: Fig. XXXVI.

1. Frontal bone; 2. parietal bone; 3. occipital bone; 4. temporal bone;
5. nasal bone; 6. malar bone; 7. superior maxillary bone; 8. inferior
maxillary bone.]

[Illustration: Fig. XXXVII.

Bones of the skull, separated; front view. 1. Frontal bone; 2. portions
of the parietal bones; 3. malar or cheek bones; 4. nasal bones; 5.
superior maxillary or bones of the upper jaw; 6. the vomer; 7. the
inferior maxillary or bone of the lower jaw.]

[Illustration: Fig. XXXVIII.

Bones of the skull separated; side view. 1. Frontal bone; 2. parietal
bone; 3. occipital bone; 4. temporal bone; 5. nasal bone; 6. malar
bone; 7. superior maxillary bone; 8. the unguis; 9. the inferior
maxillary bone.]

[Illustration: Fig. XXXIX.

Bones forming the base of the skull; viewed from the inside. 1.
Occipital bone; 2. temporal bones; 3. sphenoid bone; 4. ethmoid bone;
5. superior maxillary bones, or bones of the upper jaw; 6. malar or
cheek bones; 7. foramen magnum.]

62. The bones of the cranium are eight in number, six of which are
proper to the cranium, and two are common to it and to the face. The
six bones proper to the cranium are the frontal (fig. XXXVII. 1), the
two parietal (fig. XXXVI. 2), the two temporal (fig. XXXVIII. 4), and
the occipital (fig. XXXVIII. 3); the two common to the cranium and face
are the ethmoidal (fig. XXXIX. 4), and the sphenoidal (fig. XXXIX.
3). The frontal bone forms the entire forepart of the vault (fig.
XXXVII. 1); the two parietal form the upper and middle part of it (fig.
XXXVIII. 2); the two temporal form the lower part of the sides (fig.
XXXVIII. 4); the occipital forms the whole hinder part, together with a
portion of the base (figs. XXXVIII. 3, XXXVI. 3, XXXIX. 1); while the
ethmoidal forms the forepart, and the sphenoidal the middle part of the
base (fig. XXXIX. 3, 4).

[Illustration: Fig. XL.

2 1

Portions of the bones of the cranium; showing the corresponding
inequalities in their margins: which margins, when in apposition,
constitute the mode of union termed suture. 1. External surface of the
bone; 2. internal surface.]

[Illustration: Fig. XLI.

1

Fig. XLII.

2

1. Side view of the adult skull, showing the several bones united by
suture; 2. side view of the fœtal skull, showing the bones imperfectly
ossified, separated to some extent from each other, the interspace
being occupied by membrane. The small size of the face compared with
that of the cranium is strikingly apparent.]

63. These bones are firmly united together. The union of bones is
technically called an _articulation_ or _joint_. All joints are either
immoveable or moveable. The union of the bones of the cranium affords
an example of an immoveable articulation. Prominences and indentations,
like the teeth of a saw, are formed in the margins of the contiguous
bones (figs. XXXVIII. and XL.). At these inequalities of surface, which
are exactly adapted to each other (figs. XXXVIII. and XL.), the two
bones are in immediate apposition in such a manner as to preclude the
possibility of motion, and even to render the separation extremely
difficult. This mode of articulation is termed a _suture_. There are
certain advantages in constructing the cranium of several distinct
bones, and in uniting them in this peculiar mode. 1. The walls of the
vault are stronger than they could have been had they been formed of a
single piece. 2. In the fœtus, the bones are at some distance from each
other (fig. XLII.); at birth, they yield and overlap one another; and
in this manner they conduce to the security and ease of that event. 3.
Minute vessels pass abundantly and securely through the interstices of
the sutures to and from the interior of the cranium; in this manner,
a free communication is established between the vessels within and
without this cavity. 4. It is probable that the shock produced by
external violence is diminished in consequence of the interruption of
the vibration occasioned by the suture; it is certain that fracture is
prevented by it from extending as far as it would do in one continued
bony substance.

[Illustration: Fig. XLIII.

Section of the skull. 1. Cavity of the cranium occupied by the brain;
2. cut edge of the bones of the cranium, showing the two tables of
compact bone and the intervening spongy texture called diploë.]

64. The vault of the cranium forms a cavity which contains the
brain (fig. XLIII. and XLVIII.) The size of this cavity is invariably
proportioned to that of the organ it lodges and protects. The form and
magnitude of the cavity, and consequently the shape and size of the
cranium, depend upon the brain, and not of the brain upon the cranium.
The soft parts model and adapt to themselves the hard, and not the hard
the soft. The formation of the brain in the fœtus is anterior to that
of the case which ultimately contains it; and the hard bone is moulded
upon the soft pulp, not the pulp upon the bone. At every period of
life, on the inner surface of the cranium there are visible impressions
made by the convolutions of the brain, and the ramifications of the
arteries (figs. XXXIX. 1, 2, and XL. 2), and on its external surface
are depressions occasioned by the action of the external muscles. Nor
does the modifying power of the brain over the bones of the cranium
terminate at birth. The formation of bone, always a slow process,
is never completed until the child has attained its third or fourth
year, and often not until a much later period. At this tender age, the
bones, which in advanced life are hard and rigid, are comparatively
soft and yielding, and consequently more readily receive and retain
the impression of the convolutions and of the other projecting parts
of the brain, by which they are sometimes so deeply marked, that an
attentive examination of the inner surface of the cranium is of itself
sufficient to determine not only that some part, but to indicate the
very part of the brain which has been preternaturally active. At this
tender age, pressure, internal or external, general or partial, may
readily change the form of the cranium. If, by a particular posture,
the head of a child be unequally balanced on the spine, the brain will
press more on that side of the cranium than on the other; the organ
will expand in the direction to which it inclines; that portion of it
will become preternaturally developed, and consequently the balance of
its functions will be disturbed. An awkward way of standing or sitting,
perhaps contracted inadvertently and kept up by habit; a wry neck; any
cause that keeps the head constantly inclined to one side, may produce
this result, examples of which and of its consequences will be given
hereafter.

65. Tracing them from without inwards we see, then, that the various
coverings afforded to the brain, the central organ of the animal life,
seated in its vaulted cavity, are: 1. The tegument, consisting of the
skin and of cellular and adipose membrane. 2. Beneath the tegument,
muscles, in the forepart and at the vertex, comparatively slender and
delicate; at the sides and posteriorly, thick, strong, and powerful
(fig. XLIV.). 3. Beneath the muscles, a thin but dense membrane, termed
the pericranium, lining the external surface of the cranial bones. 4.
Beneath the pericranium, the bony substance of the cranium, consisting
of two firm and hard bony plates, with a spongy, bony structure, called
diploë, interposed between them (fig. XLIII. 2). 5. Immediately in
contact with the inner surface of the bony substance of the cranium,
and forming its internal lining, the dense and strong membrane, called
the _dura mater_, not only affording a general covering to the brain,
but sending firm partitions between individual portions of it (fig.
XLVIII. _c._). 6. A serous membrane lining the internal surface of
the dura mater, and reflected over the entire surface of the brain,
termed the arachnoid tunic. 7. A thin and delicate membrane in
immediate contact with the substance of the brain, descending between
all its convolutions, lining all its cavities and enveloping all its
fibres, called the pia mater. 8. An aqueous fluid, contained between
the arachnoid membrane and the pia mater. Skin, muscle, pericranium,
bone, dura mater, arachnoid membrane, pia mater, and aqueous fluid,
superimposed one upon another, form, then, the covering and defence of
the brain; so great is the care taken to protect this soft and tender
substance.

66. The bones of the _face_ consist of fourteen, namely, the two
superior maxillary or jaw-bones (fig. XXXVII. 5), the two malar or
cheek bones (fig. XXXVII. 3), the two nasal bones (fig. XXXVII. 4),
the two palate bones, the two ossa unguis (fig. XXXVIII. 8), the two
inferior turbinated bones, the vomer (fig. XXXVII. 6), and the inferior
maxilla or the lower jaw (fig. XXXVII. 7.) This irregular pile of bones
is divided into the superior and inferior maxilla or jaws; the superior
maxilla being the upper and immoveable portion of the face; the
inferior maxilla being the lower and moveable portion of it. Besides
these bones, the face contains thirty-two teeth, sixteen in each
jaw. The bones of the upper jaw are united together by sutures, and
the union is so firm, that they have no motion but what they possess
in common with the cranium. The lower jaw is united by a distinct
articulation with the cranium (figs. XXXIV. and XXXV.).

67. Besides the bones and the teguments, the face contains a number of
muscles, which for the most part are small and delicate (fig. XLIV.),
together with a considerable portion of adipose matter; while, as has
been stated, the face and head together contain all the senses, with
the exception of that of touch, which is diffused, more or less, over
the entire surface of the body.

[Illustration: Fig. XLIV.

Muscles of the face.]

68. The second great division of the body, termed the TRUNK, extends
from the first bone of the neck to that called the pubis in front, and
to the lower end of the coccyx behind (fig. XXXIV. 2). It is subdivided
into the thorax, the abdomen, and the pelvis (fig. XLV.).

69. The _thorax_ or _chest_ extends above from the first bone of
the neck, by which it is connected with the head, to the diaphragm
below, by which it is divided from the abdomen (figs. XLV. and LXI.).
It consists partly of muscles and partly of bones; the muscular and
the osseous portions being in nearly equal proportions. Both together
form the walls of a cavity in which are placed the central organs of
circulation and respiration (fig. LX. 2, 5). The chief boundaries of
the cavity of the thorax before, behind, and at the sides, are osseous
(fig. XLV.); being formed before, by the sternum or breast-bone (fig.
XLV. 6); behind, by the spinal column or back bone (fig. XLV. 2, 4);
and at the sides, by the ribs (fig. XLV. 7). Below, the boundary is
muscular, being formed by the diaphragm (fig. LXI. 2), while above the
thorax is so much contracted (fig. XLV.), that there is merely a space
left for the passage of certain parts which will be noticed immediately.

70. The figure of the thorax is that of a cone, the apex being above
(fig. XLV.), through the aperture of which pass the tubes that lead
to the lungs and stomach, and the great blood-vessels that go to and
from the heart (fig. LX.). The base of the cone is slanting, and is
considerably shorter before than behind, like an oblique section of the
cone (fig. XLV.).

71. The osseous portion of the walls of the thorax is formed behind by
the spinal column, a range of bones common indeed to all the divisions
of the trunk; for it constitutes alike the posterior boundary of the
thorax, abdomen, and pelvis (fig. XLV. 2, 4, 6). It is composed of
thirty distinct bones, twenty-four of which are separate and moveable
on one another, and on this account are called true vertebræ (fig. XLV.
2, 4); the other five, though separate at an early period of life, are
subsequently united into a single solid piece, called the sacrum (fig.
XLV. 5). The bones composing this solid piece, as they admit of no
motion on each other, are called false vertebræ (fig. XLV. 5). To the
extremity of the sacrum is attached the last bone of the series, termed
the coccyx (fig. XXXV.).

72. From above downwards, that is, from the first bone of the neck to
the first bone of the sacrum, the separate bones forming the column
progressively increase in size; for this column is the chief support
of the weight of the head and trunk, and this weight is progressively
augmenting to this point (fig. XLV. 2, 4). From the sacrum to the
coccyx, the bones successively diminish in size, until, at the
extremity of the coccyx, they come to a point (fig. XXXV.). The spinal
column may therefore be said to consist of two pyramids united at their
base (fig. XLV. 4, 5). The superior pyramid is equal in length to about
one third of the height of the body, and it is this portion of the
column only that is moveable.

73. The two surfaces of the spinal column, the anterior and the
posterior, present a striking contrast (figs. XXXIV. and XXXV.). The
anterior surface, which in its whole extent is rounded and smooth, is
broad in the region of the neck, narrow in the region of the back, and
again broad in the region of the loins (fig. XLV. 2, 4.). It presents
three curvatures (fig. XLV. 2, 4); the convexity of that of the neck
being forwards, that of the back backwards, and that of the loins again
forwards (fig. XLV. 2, 4).

74. From the posterior surface of the column, which is every where
irregular and rough, spring, along the median line, in regular series,
strong, sharp, and pointed projections of bone (fig. XXXV.), which
from being sharp and pointed, like elongated spines, are called
spinous processes, and have given name to the whole chain of bones.
These processes afford fixed points for the action of powerful
muscles. Extending the whole length of the column, from the base of
the skull to the sacrum, on each side of the spinous processes, are
deep excavations, which are filled up with the powerful muscles that
maintain the trunk of the body erect.

75. From the lateral surfaces of the column likewise spring short but
strong projections of bone, termed transverse processes, which also
give attachment to powerful muscles (fig. XLVI.).

[Illustration: Fig. XLV.

Bones of the trunk. 1. Spinal column; 2. the seven cervical vertebræ;
3. the twelve dorsal vertebræ; 4. the five lumbar vertebræ; 5. the
sacrum; 6. the sternum; 7. the true ribs; 8. the false ribs; 9. the
clavicle; 10. the scapula; 11. the ilium; 12. the ischium; 13. the
pubes; 14. the acetabulum; 15. the brim of the pelvis.]

76. The separate bones of the series have a kind of turning motion on
each other; hence each is called a vertebra, and the name of vertebral
column is often given to the entire series, as well as that of spinal
column. That portion of the column which forms the neck consists of
seven distinct bones, called cervical vertebræ (fig. XLV. 2); that
portion which forms the back consists of twelve, called dorsal vertebræ
(fig. XLV. 3); that portion which forms the loins consists of five,
called lumbar vertebræ (fig. XLV. 4). Between each of these classes of
vertebræ there are specific differences, but they need not be described
here: all that is necessary to the present purpose is an account of the
structure which is common to every vertebra.

77. By inspecting fig. XLVI. 1, it will be seen that the upper and
under edges of each vertebra consist of a ring of bone, of a firm
and compact texture, rendering what may be called the body of the
vertebra exceedingly strong (fig. XLVI. 3). This ring of bone forms a
superficial depression (fig. XLVI. 2), for the reception of a peculiar
substance, immediately to be described, which is interposed between
each vertebra (fig. XLVII. 2).

78. The anterior surface of the body of the vertebra is convex (fig.
XLVI. 3); its posterior surface is concave (fig. XLVI. 4); from the
posterior surface springs a bony arch (figs. XLVI. 5 and LIII. 1),
which, together with the posterior concavity, forms an aperture of
considerable magnitude (fig. XLVI. 6), a portion of the canal for the
passage of the spinal cord (figs. XLVII. 3, and XLIX. 3).

[Illustration: Fig. XLVI.

View of some of the vertebræ, which by their union form the spinal
column.

_a._ A vertebra of the neck; _b._ a vertebra of the back; a vertebra of
the loins.

1. Ring of compact bone forming, 3, the body of the vertebra; 2.
superficial depression for the reception of the intervertebral
cartilage; 3. anterior surface of the body of the vertebra; 4.
posterior surface; 5. bony arch; 6. opening for the passage of the
spinal cord; 7. opening for the passage of the spinal nerves; 8.
articulating processes by which the vertebræ are joined to each other;
9. two dorsal vertebræ united, showing the arrangement of, 10, the
spinous processes; 11. a portion of a rib articulated with the side of
the vertebra.]

79. Both the upper and under edges of the arch form a notch (fig. XLVI.
7.), which, together with a corresponding notch in the contiguous
vertebra, completes another aperture rounder and smaller than the
former, but still of considerable size (fig. XLVI. 7.), the passage of
the spinal nerves (fig. XLVII. 3).

80. From both the upper and under sides of the arch proceed two short
but strong projections of bone (fig. XLVI. 8.), termed the articulating
processes, because it is chiefly by these processes that the vertebræ
are connected together. From the beginning to the end of the series,
the two upper processes of the one vertebra are united with the two
lower processes of the vertebra immediately above it (fig. XLVI. 9),
and around the edges of all the articulating processes are visible
rough lines, which mark the places to which the articulating ligaments
are attached.

81. No vertebra, except the first, rests immediately upon its
contiguous vertebra (fig. XLV. 2, 4). Each is separated from its fellow
by a substance of a peculiar nature interposed between them, termed the
intervertebral substance (figs. XLVII. 2, and L. 2). This substance
partakes partly of the nature of cartilage, and partly of that of
ligament. It is composed of concentric plates, formed of oblique fibres
which intersect each other in every direction. This substance, for
about a quarter of an inch from its circumference towards its centre,
is tough, strong, and unyielding; then it becomes softer, and is
manifestly elastic; and so it continues until it approaches the centre,
when it becomes pulpy, and is again inelastic. The exterior tough and
unyielding matter is for the firmness of the connexion of the several
vertebræ with each other; the interior softer and elastic matter is for
the easy play of the vertebræ upon each other; the one for security,
the other for pliancy. And the adjustment of the one to the other is
such as to combine these properties in a perfect, manner. The quantity
of the unyielding substance is not so great as to produce rigidity;
the quantity of the elastic substance is not so great as to occasion
insecurity. The firm union of its solid matter renders the entire
column strong; the aggregate elasticity of its softer substance renders
it springy.

[Illustration: Fig. XLVII.

1. One of the Lumbar vertebræ. 2. Intervertebral substance. 3. A
portion of the spinal cord in its canal.]

82. The column is not constructed in such a manner as to admit of an
equal degree of motion in every part of it. Every thing is contrived
to give to that portion which belongs to the neck freedom of motion,
and, on the contrary, to render that portion which belongs to the back
comparatively fixed. In the neck the mechanism of the articulating
processes is such as to admit of an equal degree of sliding motion
forwards, backwards, and from side to side, together with a turning
motion of one bone upon another; at the same time, the intervertebral
substance between the several vertebræ is thick. In consequence of this
mechanism, we can touch the breast with the chin, the back with the
hind head, and the shoulders with the ear, while we can make the head
describe more than a semicircle. But, in the back, the articulating
processes are so connected as to prevent the possibility of any motion,
either forwards or backwards, or any turning of one vertebra upon
another, while the intervertebral substance is comparatively thin (fig.
XLV. 2, 4). That portion of the column which belongs to the back is
intended to afford a fixed support for the ribs, a support which is
indispensable to their action in the function of respiration. In the
loins, the articulating processes are so connected as to admit of a
considerable degree of motion in the horizontal direction, and from
side to side, and the intervertebral substance here progressively
increases in thickness to the point at which the upper portion of the
column is united to the sacrum (fig. XLV. 2, 4), where the degree of
motion is extensive.

83. The canal for the spinal cord, formed partly by the concavity in
the posterior surface of the vertebra, and partly by the arch that
springs from it (fig. XLVI. 6.), is lined by a continuation of the
dense and strong membrane that constitutes the internal periosteum
of the cranium, the dura mater (fig. XLVIII. _c_), which, passing
out of the opening in the occipital bone, called the foramen magnum
(figs. XXXIX. 7, and XLIX. 3), affords a smooth covering to the canal
throughout its whole extent.

[Illustration: Fig. XLVIII.

_a._ The scalp, turned down.

_b._ The cut edge of the bones of the skull.

_c._ The external strong membrane of the brain (Dura Mater) suspended
by a hook.

_d._ The left hemisphere of the brain, showing its convolutions.

_e._ The superior edge of the right hemisphere.

_f._ The fissure between the two hemispheres.]


[Illustration: Fig. XLIX.

1. Hemispheres of the brain proper, or cerebrum; 2. hemispheres of the
smaller brain, or cerebellum; 3. spinal cord continuous with the brain,
and the spinal nerves proceeding from it on each side.]

84. The spinal cord itself, continuous with the substance of the
brain, passes also out of the cranium through the foramen magnum into
the spinal canal (fig. XLIX. 3), enveloped in the delicate membranes
that cover it, and surrounded by the aqueous fluid contained between
those membranes. The size of the spinal canal, accurately adapted
to that of the spinal cord, which it lodges and protects, is of
considerable size, and of a triangular shape in its cervical portion
(fig. XLIX. 3), smaller and rounded in its dorsal portion (fig. XLIX.
3), and again large and triangular in its lumbar portion (fig. XLIX. 3).

85. The spinal column performs several different, and apparently
incompatible, offices.

First, it affords a support and buttress to other bones. It sustains
the head (fig. XXXIV. 1); it is a buttress to the ribs (fig. XLVI. 7);
through the sternum and ribs it is also a buttress to the superior, and
through the pelvis, to the lower, extremities (fig. XXXIV. 2, 3, 4).

Secondly, it affords a support to powerful muscles, partly to those
that maintain the trunk of the body in the erect posture against the
force of gravitation, and partly to those that act upon the superior
and inferior extremities in the varied, energetic, and sometimes
long-continued movements they execute.

Thirdly, it forms one of the boundaries of the great cavities that
contain the chief organs of the organic life. To the support and
protection of those organs it is specially adapted; hence the surface
in immediate contact with them is even and smooth; hence its different
curvatures, convexities, and concavities, have all reference to their
accommodation; hence in the neck it is convex (fig. XLV. 2), in order
to afford a firm support to the esophagus, the wind-pipe, the aorta,
and the great trunks of the venous system (fig. LX. 3, 4); in the back
it is concave, in order to enlarge the space for the dilatation of
the lung in the act of inspiration (figs. XLV. 3, and LX. 5); in the
loins it is convex, in order to sustain and fix the loose and floating
viscera of the abdomen (figs. XLV. 4, and LX. 6, 7, 8, 9); in the
pelvis it is concave, in order to enlarge the space for lodging the
numerous delicate and highly-important organs contained in that cavity
(fig. XLV. 5).

Fourthly, it forms the osseous walls of a canal (figs. XLVI. 6, and
XLVII. 3) for the lodgment and protection of the soft and tender
substance of the spinal cord, one of the great central masses of the
nervous system, the seat of the animal life (fig. XLIX. 3).

Fifthly, it affords in its osseous walls secure apertures for the
passage of the spinal nerves (figs. XLVI. 7, and XLIX. 3), by which
impressions are transmitted from the organs to the spinal cord and
brain, in the function of sensation; and from the spinal cord and brain
to the organs in the function of volition.

86. For the due performance of these offices, it is indispensable that
it should be firm, rigid, strong, and yet to a certain extent readily
flexible in every direction. By what mechanism is it endowed with these
apparently incompatible properties?

87. By means of the ring of compact bone, which forms so large a part
of its body (fig. XLVI. 1) it is rendered firm, rigid, and strong. By
means of its numerous separate pieces, exactly adjusted to each other,
and dove-tailed into one another, an increase of strength is gained,
such as it would not have been possible to communicate to a single
solid piece. By the same mechanism, some degree of flexibility is also
obtained; each separate bone yielding to some extent, which, though
slight in a single bone, becomes considerable in the twenty-four.

88. But the flexibility required is much greater than could be
obtained by this expedient alone. A rigid and immoveable pile of bones,
in the position of the spinal column, on which all the other parts of
the body rest, and to which they are directly or indirectly attached,
would necessarily have rendered all its movements stiff and mechanical;
and every movement of every kind impossible, but in a given direction.
That the movements of the body may be easy, free, and varied; that it
may be possible to bring into play new and complex combinations of
motion at any instant, with the rapidity of the changes of thought,
at the command of the impulses of feeling, it is indispensable that
the spinal column be flexible in every direction, forwards, backwards,
and at the sides: it is equally indispensable that it be thus capable
of yielding, without injuring the spinal cord; without injuring the
spinal nerves; without injuring the thoracic and abdominal viscera; and
without injuring the muscles of the trunk and extremities. The degree
in which it possesses this power of flexibility, and the extent to
which, by the cultivation of it, it is sometimes actually brought, is
exemplified in the positions and contortions of the posture-master and
the tumbler. It is acquired by means of the intervertebral substance,
the compressible and elastic matter interposed between the several
vertebræ. So compressible is this substance, that the human body is
half an inch shorter in the evening than in the morning, having lost
by the exertions of the day so much of its stature; yet, so elastic is
this matter, that the stature lost during the day is regained by the
repose of the night. The weight of the body pressing in all directions
upon the spinal column; muscles, bones, cartilages, ligaments,
membranes, with all their vessels and all the fluids contained in
them; the weight of all these component parts of the head, trunk, and
extremities, pressing, without the cessation of an instant, during all
the hours of vigilance, upon the intervertebral substance, compresses
it; but this weight, being taken off during the night, by the recumbent
posture of the body, the intervertebral substance, in consequence of
its elasticity, regains its original bulk, and of course the spinal
column its original length.

89. But the flexibility acquired through the combined properties of
compressibility and elasticity is exceedingly increased by the action
of the pulpy and inelastic matter in the centre of the intervertebral
substance; this matter serving as a pivot to the vertebræ, facilitating
their motion on each other. Its effect has been compared to that of
a bladder partly filled with water, placed between two trenchers; in
this case, the approximation of the circumference of the two trenchers
on one side, would instantly displace a portion of the water on that
side, which would occupy the increasing space on the other, with the
effect of facilitating the change, in every possible direction, of
the position of the two trenchers in relation to each other. To this
effect, however, it is indispensable that the matter immediately around
this central pivot should be, not like itself, rigid and unyielding,
but compressible and elastic. It is an interesting fact, that since
this illustration was suggested, it has been discovered that this
very arrangement is actually adopted in the animal body. In certain
animals, in the very centre of their intervertebral substance, there
has been actually found a bag of water, with a substance immediately
surrounding the bag, so exceedingly elastic, that when the bag is cut,
the fluid contained in it is projected to the height of several feet in
a perpendicular stream.

90. But besides securing freedom and extent of motion, the
intervertebral substance serves still another purpose, which well
deserves attention.

Firmness and strength are indispensable to the fundamental offices
performed by the column; and to endow it with these properties, we
have seen that the external concentric layers of the intervertebral
substance are exceedingly tough and that they are attached to the
bodies of the vertebræ, which are composed of dense and compact bone.
But than dense and compact bone, nothing can be conceived better
calculated to receive and transmit a shock or jar on the application
of any degree of force to the column. Yet such force must necessarily
be applied to it in every direction, from many points of the body,
during almost every moment of the day; and did it actually produce a
corresponding shock, the consequence would be fatal: the spinal cord
and brain would be inevitably killed; for the death of these tender and
delicate substances may be produced by a violent jar, although not a
particle of the substances themselves be touched. A blow on the head
may destroy life instantaneously, by what is termed concussion; that
is, by the communication of a shock to the brain through the bones of
the cranium. The brain is killed; but on careful examination of the
cerebral substance after death, not the slightest morbid appearance
can be detected: death is occasioned merely by the jar. A special
provision is made against this evil, in the structure of the bones
of the cranium, by the interposition between its two compact plates
of the spongy substance called diploë (fig. XLIII. 2); and this is
sufficient to prevent mischief in ordinary cases. A great degree of
violence applied directly to the head is not common: when it occurs
it is accidental: thousands of people pass through life without ever
having suffered from it on a single occasion: but every hour, in the
ordinary movements of the body, and much more in the violent movements
which it occasionally makes, a degree of force is applied to the spinal
column, and through it transmitted to the head, such as, did it produce
a proportionate shock, would inevitably and instantly destroy both
spinal cord and brain. The evil is obviated partly by the elastic, and
partly by the non elastic properties of the matter interposed between
the several layers of compact bone. By means of the elastic property
of this matter, the head rides upon the summit of the column as upon a
pliant spring, while the canal of the spinal cord remains secure and
uninvaded. By means of the soft and pulpy portion of this matter, the
vibrations excited in the compact bone are absorbed point by point as
they are produced: as many layers of this soft and pulpy substance, so
many points of absorption of the tremors excited in the compact bone;
so many barriers against the possibility of the transmission of a shock
to the delicate nervous substance.

91. Alike admirable is the mechanism by which the separate pieces
of the column are joined together. If but one of the bones were to
slip off its corresponding bone, or to be displaced in any degree,
incurable paralysis, followed ultimately by death, or instantaneous
death, would happen; for pressure on the spinal cord in a certain part
of its course is incompatible with the power of voluntary motion, and
with the continuance of life for any protracted term; and in another
part of its course, with the maintenance of life beyond a few moments.
To prevent such consequences, so great is the strength, so perfect the
attachment, so unconquerable the resistance of that portion of the
intervertebral substance which surrounds the edge of the bodies of the
vertebræ, that it will allow the bone itself to give way rather than
yield. Yet such is the importance of security to this portion of the
frame, that it is not trusted to one expedient alone, adequate as that
might seem. Besides the intervertebral substance, there is another
distinct provision for the articulation of the bodies of the vertebræ.
Commencing at the second cervical vertebra, in its fore part, and
extending the whole length of the column to the sacrum, is a powerful
ligament, composed of numerous distinct longitudinal fibres (fig. L.),
which are particularly expanded over the intervals between the bones
occupied by the intervertebral substance (figs. L. 1, and LI. 2, 2).
This ligament is termed the _common anterior vertebral_, beneath which,
if it be raised from the intervertebral substance, may be seen small
_decussating_ fibres, passing from the lower edge of the vertebra
above, to the upper edge of the vertebra below (fig. L. 3), from which
circumstance these fibres are termed _crucial_.

[Illustration: Fig. L.

1. Common anterior ligament; 2. intervertebral substance. The anterior
ligament is removed to exhibit (3.) the crucial fibres passing over it.]

[Illustration: Fig. LI.

1. Portion of the occipital bone; 2. common anterior ligament.]

92. Corresponding with the ligament on the anterior, is another on
the posterior part of the spine (fig. LII. 1), which takes its origin
from the foramen magnum (fig. LII. 1); descends from thence, within the
vertebral canal, on the posterior surface of the bodies of the vertebra
(fig. LII. 1), and extends to the sacrum. This ligament is termed the
_common posterior vertebral_, which, besides adding to the strength of
the union of the bodies of the vertebræ, prevents the column itself
from being bent too much forward.

[Illustration: Fig. LII.

1. Posterior vertebral ligament.]

93. Moreover, the bony arches of the vertebræ (fig. LIII. 1) are
connected by means of a substance partly ligamentous, and partly
cartilaginous (fig. LIII. 2), which, while it is extremely elastic, is
capable of resisting an extraordinary degree of force.

[Illustration: Fig. LIII.

1. Arches of the vertebræ seen from within; 2. ligaments connecting
them.]

94. And in the last place, the articular processes form so many
distinct joints, each being furnished with all the apparatus of a
moveable joint, and thus possessing the ordinary provision for the
articulation of bones, in addition to the whole of the foregoing
securities.

95. "In the most extensive motion of which the spinal column is
capable, that of flexion, the common anterior ligament is relaxed; the
fore part of the intervertebral substance is compressed, and its back
part stretched; while the common posterior ligament is in a state of
extension. In the _extension_ of the column the state of the ligaments
is reversed; those which were extended being in their turn relaxed,
while the common anterior vertebral is now put upon the stretch. In the
_lateral inclination_ of the column, the intervertebral substance is
compressed on that side to which the body is bent. In the _rotatory_
motion of the column, which is very limited in all the vertebræ, but
more particularly in the dorsal, in consequence of their attachment to
the ribs, the intervertebral substance is contorted, as are likewise
all the ligaments. All the motions of the column are capable of being
aided to a great extent by the motion of the pelvis upon the thighs."

96. "The number and breadth of the attachments of these bones,"
says an accomplished anatomist and surgeon,[4] "their firm union by
ligament, the strength of their muscles, the very inconsiderable
degree of motion which exists between any two of them, and lastly, the
obliquity of their articular processes, especially in the dorsal and
lumbar vertebræ, render dislocation of them, at least in those regions,
impossible without fracture; and I much doubt whether dislocation even
of the cervical vertebræ ever occurs without fracture, either through
their bodies or their articular processes. The effects of each of these
accidents would produce precisely the same injury to the spinal marrow,
and symptoms of greater or less importance, according to the part of
the spinal column that is injured. Death is the immediate consequence
if the injury be above the third cervical vertebra, the necessary
paralysis of the parts to which the phrenic and intercostal nerves
are distributed causing respiration instantly to cease. If the injury
be sustained below the fourth cervical vertebra, the diaphragm is
still capable of action, and dissolution is protracted. The symptoms,
in fact, are less violent in proportion as the injury to the spinal
marrow is further removed from the brain; but death is the inevitable
consequence, and that in every case at no very distant period."

97. So the object of the construction of the spinal column being
to combine extent and freedom of motion with strength, and it being
necessary to the accomplishment of this object to build up the column
of separate pieces of bone, the connecting substances by which the
different bones are united are constituted and disposed in such a
manner as to prove absolutely stronger than the bones themselves. Such
is the structure of this important portion of the human body considered
as a piece of mere mechanism; but our conception of its beauty and
perfection would be most inadequate if we did not bear in mind, that
while the spinal column performs offices so varied and apparently so
incompatible, it forms an integrant portion of a living machine: it is
itself alive: every instant, blood-vessels, absorbents and nerves, are
nourishing, removing, renewing, and animating every part and particle
of it.

98. The anterior boundary of the thorax is formed by the bone called
the sternum, or the breast-bone, which is broad and thick at its upper,
and thin and elongated at its lower extremity (figs. XLV. 6, and
LIV.), where it gives attachment to a cartilaginous appendix, which
being pointed and somewhat like a broadsword, is called the ensiform
cartilage.

[Illustration: Fig. LIV.

Anterior view of the sternum.]

99. Its position is oblique, being near the vertebral column at the
top, and distant from it at the bottom (fig. XLV. 6). Its margins
are thick, and marked by seven depressions, for the reception of the
cartilages of the seven true ribs (fig. LIV). Its anterior surface is
immediately subjacent to the skin, and gives attachment to powerful
muscles, which act on the superior extremities: its posterior surface
is slightly hollowed in order to enlarge the cavity of the thorax (fig.
LV.).

[Illustration: Fig. LV.

Posterior view of the sternum.]

100. The thorax is bounded at the sides by the ribs, which extend like
so many arches between the spinal column and the sternum (fig. XLV. 7,
8). They are in number twenty-four, twelve on each side, of which the
seven upper are united to the sternum by cartilage, and are called true
ribs (fig. XLV. 7); the cartilages of the remaining five are united
with each other and are not attached to the sternum; these are called
false ribs (fig. XLV. 8): all of them are connected behind to the
spinal column (fig. XXXV.).

101. The ribs successively and considerably increase in length as far
as the seventh, by which the cavity they encompass is enlarged; from
the seventh they successively diminish in length, and the capacity of
the corresponding part of the cavity is lessened. The direction of the
ribs from above downwards is oblique (fig. XLV. 7, 8). Their external
or anterior surface is convex (fig. XLV. 7, 8); their internal or
posterior surface is concave: by the first their strength is increased;
by the second the general cavity of the thorax is enlarged (fig. XLV.
7, 8). Their upper margin is smooth and rounded, and gives attachment
to a double layer of muscles, called the intercostal, placed in the
intervals that separate the ribs from each other (fig. LIX.). Along
the lower margin is excavated a deep groove, for the lodgment and
protection of the intercostal vessels.

102. The ribs are connected with the spinal column chiefly by what is
termed the _anterior ligament_ (fig. LVI. 1), which is attached to the
head of the rib (fig. LVI.), and which, dividing into three portions
(fig. LVI. 1), firmly unites every rib to two of the vertebræ, and
to the intervertebral substance (fig. LVI. 1). This articulation is
fortified by a second ligament (fig. LVI. 2), also attached to a head
of the rib, termed the _interarticular_ (fig. LVI. 2), and by three
others, one of which is attached on the fore part, and the two others
in the back part, to the neck of the rib (fig. LVII. 1).

[Illustration: Fig. LVI.

Ligaments connecting the ribs to the spinal column. 1. anterior
ligaments; 2. interarticular ligament; 3. ligaments of the necks of the
ribs.]

The cartilages of the seven superior ribs are attached to the sternum
by a double layer of ligamentous fibres, termed the _anterior and the
posterior ligaments of the sternum_ (fig. LVIII.). So strong are the
bands which thus attach the ribs to the spinal column and the sternum,
that the ribs cannot be dislocated without fracture. "Such at least is
the case in experiments upon the dead body, where, though the rib be
subjected to the application of force by means of an instrument best
calculated to detach its head from the articulation, yet it is always
broken."

[Illustration: Fig. LVII.

1, &c. Ligaments connecting the ribs to the vertebræ behind.]

While thus firmly attached to their points of support, the ligaments,
which fix them, are so disposed as to render the ribs capable of being
readily moved upwards and downwards: upwards in inspiration; downwards
in expiration; and it is by this alternate action that they enlarge and
diminish the cavity of the thorax in the function of respiration.

[Illustration: Fig. LVIII.

Ligaments joining the cartilages of the ribs to the sternum.]

103. Such are the boundaries of the cavity of the thorax as far as
its walls are solid. The interspaces between these solid portions at
the sides are filled up by muscles, principally by those termed the
intercostal (fig. LIX.); below, the boundary is formed by the diaphragm
(fig. LXI. 2); while above, as has been already stated (69), the cavity
is so contracted as only to leave an opening for the passage of certain
parts to and from the chest.

[Illustration: Fig. LIX.

A view of the muscles called _Intercostals_, filling up the spaces
between the ribs.]

104. The inner surface of the walls of the thorax, in its whole
extent, is lined by a serous membrane, exceedingly thin and delicate,
but still firm, called the pleura. The same membrane is reflected over
the organs of respiration contained in the cavity, so as to give them
an external coat. The membrane itself is every where continuous, and
every where the same, whether it line the containing or the contained
parts; but it receives a different name as it covers the one or the
other: that portion of it which lines the walls of the cavity being
called the costal pleura (fig. LXI. _a_), while that which covers the
organs contained in the cavity is termed the pulmonary pleura (fig. LX.
5, 1).

105. A fold of each pleura passes directly across the central part
of the cavity of the thorax; extending from the spinal column to the
sternum, and dividing the general cavity into two. This portion of the
pleura is called the mediastinum, from its situation in the centre
of the thorax, and it so completely divides the thoracic cavity into
two, that the organs on one side of the chest have no communication
with those of the other; so that there may be extensive disease in one
cavity (for example, a large accumulation of water,) while the other
may be perfectly sound.

106. The main organs contained in the cavity of the thorax are the
lungs with their air tube; the heart with its great vessels; and the
tube passing from the mouth to the stomach (fig. LX.).

107. The two lungs occupy the sides of the chest (fig. LX. 5). They
are completely separated from each other by the membranous partition
just described, the mediastinum. Between the two folds of the
mediastinum, namely, in the middle of the chest, but inclining somewhat
to the left side, is placed the heart, enveloped in another serous
membrane, the pericardium (fig. LX. 2, 1).

108. The lungs are moulded to the cavities they fill; whence their
figure is conical, the base of the cone being downwards, resting on the
diaphragm (fig. LX. 5, _b_); and the apex upwards, towards the neck
(fig. LX. 5).

109. That surface of each lung which corresponds to the walls of the
chest is convex in its whole extent (fig. LX. 5); on the contrary, that
surface which corresponds to the mediastinum is flattened (fig. LX.
5). The basis of the lung is concave, adapted to the convexity of the
diaphragm on which it rests (fig. LX. 5).

110. The air-vessel of the lungs, termed the bronchus, together with
the blood-vessels and nerves, enter the organ at its flattened side,
not exactly in the middle, but rather towards the upper and back part.
This portion is termed the root of the lung.

111. The lungs are attached to the neck by the trachea (fig. LX. 4),
the continuation of which forms the bronchus; to the spinal column by
the pleura, and to the heart by the pulmonary vessels (fig. LX. 3,
_d_): their remaining portion is free and unattached.

112. In the living body, the lungs on each side completely fill the
cavity of the chest, following passively the movements of its walls,
and accurately adapting themselves to its size, whether its capacity
enlarge in inspiration, or diminish in expiration, so that the external
surface of the lung (the pulmonary pleura) is always in immediate
contact with the lining membrane of the walls of the cavity (the costal
pleura); consequently, during life, there is no cavity, the chest being
always completely full.

[Illustration: Fig. LX.

_a._ The cut edges of the ribs, forming the lateral boundaries of the
cavity of the thorax.

_b._ The diaphragm, forming the inferior boundary of the thorax, and
the division between the thorax and the abdomen.

_c._ The cut edges of the abdominal muscles, turned aside, exposing the
general cavity of the abdomen.

1. The cut edge of the pericardium turned aside.

2. The heart.

3. The great vessels in immediate connexion with the heart.

4. The trachea, or wind-pipe.

5. The lungs.

6. The liver.

7. The stomach.

8. The large intestine.

9. The small intestines.

10. The urinary bladder.]

113. The anterior surface of the pericardium, the bag which envelopes
the heart, lies immediately behind the sternum, and the cartilages of
the second, third, fourth, and fifth ribs, covered at its sides by the
pleura, and firmly attached below to the diaphragm (fig. LX. 1).

114. Surrounded by its pericardium, within the mediastinum, the heart
is placed nearly in the centre of the chest, but its direction is
somewhat oblique, its apex being directly opposite to the interval
between the fifth and sixth ribs on the left side (fig. LX. 2); while
its basis is directed upwards, backwards, and towards the right (fig.
LX. 2). That portion of its surface which is presented to view on
opening the pericardium is convex (fig. LX. 2); but its opposite
surface, namely, that which rests upon the part of the pericardium
which is attached to the diaphragm, is flattened (fig. LX. 1). It is
fixed in its situation partly by the pericardium and partly by the
great vessels that go to and from it. But under the different states
of expiration and inspiration, it accompanies, in some degree, the
movements of the diaphragm; and in the varied postures of the body,
the heart deviates to a certain extent from the exact position here
described.

115. The second division of the trunk, the _abdomen_, is bounded above
by the diaphragm (fig. LXI. 2), below by the pelvis (fig. LXI. 3),
behind and at the sides by the vertebræ and muscles of the loins (fig.
LXIII.), and before by the abdominal muscles (fig. LXIII. 9).

116. The organ which forms the superior boundary of the abdomen, the
diaphragm (midriff), is a circular muscle, placed transversely across
the trunk, nearly at its centre (fig. LXI. 2). It forms a vaulted
partition between the thorax and the abdomen (fig. LXI. 2). All around
its border it is fleshy (fig. LXI. 2); towards its centre it is
tendinous (fig. LXI. 2); the surface towards the abdomen is concave
(fig. LXI. 2); that towards the thorax convex (fig. LXI. 2); while its
middle tendinous portion ascends into the thorax as high as the fourth
rib (fig. LXI. 2).

[Illustration: Fig. LXI.

View of the diaphragm. 1. Cavity of the thorax; 2. diaphragm separating
the cavity of the thorax from that of the abdomen; 3. cavity of the
pelvis.]

117. The diaphragm is perforated by several apertures, for the
transmission of tubes and vessels, which pass reciprocally between the
thorax and abdomen (fig. LXII.).

1. A separate aperture is formed to afford an exit from the thorax
of the aorta, the common source of the arteries (fig. LXII. 2), and
an entrance into the thorax of the thoracic duct, the tube that bears
the digested aliment to the heart. 2. A little to the left of the
former, there is another aperture, through which passes the esophagus
or gullet (fig. LXII. 3), the tube that conveys the food from the mouth
to the stomach. 3. On the right side, in the tendinous portion of the
diaphragm, very carefully constructed, is a third aperture for the
passage of the vena cava (fig. LXII. 4), the great vessel that returns
the blood to the heart from the lower parts of the body.

[Illustration: Fig. LXII.

View of the diaphragm with the tubes that pass through it. 1. Arch
of the diaphragm; 2. the trunk of the aorta passing from the chest
into the abdomen; 3. the esophagus passing from the chest through the
diaphragm to the stomach; 4. the vena cava, the great vein that returns
the blood to the heart from the lower parts of the body, passing from
the abdomen, into the chest, in its way to the right side of the heart;
5. 6. muscles that arise in the interior of the trunk and that act upon
the thigh; 5. the muscle called psoas; 6. the muscle called iliacus.]

118. The partition formed by the diaphragm between the thorax and
abdomen, though complete, is moveable; for as the diaphragm descends in
inspiration and ascends in expiration, it proportionally enlarges or
diminishes the cavities between which it is placed; consequently, the
actual magnitude of these cavities varies every moment, and the size of
the one is always in the inverse ratio of that of the other.

119. Between the abdomen and the pelvis there is no separation; one
cavity is directly continuous with the other (fig. LXI. 3); but along
the inner surface of the expanded bones, which form a part of the
lateral boundary of the abdomen, there is a prominent line, termed
the brim of the pelvis (fig. XLV. 15), marking the point at which the
abdomen is supposed to terminate and the pelvis to commence.

120. Behind and at the sides the walls of the abdomen are completed
partly by the lumbar portion of the spinal column and partly by the
lumbar muscles (fig. XLV. 4), and before by the abdominal muscles (fig.
LXIII. 9).

121. The inner surface of the walls of the abdomen is lined throughout
by a serous membrane, termed the peritoneum (fig. LXIII.). From the
walls of the abdomen, the peritoneum is reflected upon the organs
contained in the cavity, and is continued over them so as to form their
external coat. The peritoneum also descends between the several organs,
connecting them together, and holding them firmly in their situation;
and it likewise forms numerous folds, in which are embedded the vessels
and nerves that supply the organs. It secretes a serous fluid, by
which its own surface and that of the organs it covers is rendered
moist, polished, and glistening, and by means of which the organs
glide smoothly over it, and over one another in the various movements
of the body, and are in constant contact without growing together. In
structure, distribution, and function, the peritoneum is thus perfectly
analogous to the pleura.

122. Like the thorax, the abdomen is always completely full. When
the diaphragm is in action, it contracts. When the diaphragm is
in the state of contraction, the abdominal and lumbar muscles are
in the state of relaxation. By the contraction of the diaphragm,
the organs contained in the abdomen are pushed downwards, and the
anterior and lateral walls of the cavity being at this moment in
a state of relaxation, they readily yield, and, consequently, the
viscera are protruded forwards and at the sides. But the abdominal
and lumbar muscles in their turn contract, the diaphragm relaxing;
and, consequently, the viscera, forced from the front and sides of the
abdomen, are pushed upwards, together with the diaphragm, into the
cavity of the thorax. A firm and uniform pressure is thus at all times
maintained upon the whole contents of the abdomen: there is an exact
adaptation of the containing to the contained parts, and of one organ
to another. No space intervenes either between the walls of the abdomen
and the organs they enclose, or between one organ and another: so that
the term cavity does not denote a void or empty space, but merely the
extent of the boundary within which the viscera are contained.

123. The contents of the abdomen consist of the organs which belong to
the apparatus of digestion, and of those which belong to the apparatus
of excretion.

124. The organs which belong to the apparatus of digestion are—1. The
stomach (fig. LXIII. 2) 2. The duodenum (fig. LXIII. 4). 3. The jejunum
(fig. LXIII. 5). 4. The ilium (fig. LXIII. 5). The three last organs
are called the small intestines, and their office is partly to carry on
the digestion of the aliment commenced in the stomach, and partly to
afford an extended surface for the absorption of the nutriment as it is
prepared from the aliment. 5. The pancreas (fig. LXIV. 5). 6. The liver
(fig. LXIV. 2). 7. The spleen (fig. LXIV. 4). The three last organs
truly belong to the apparatus of digestion, and their office is to
co-operate with the stomach and the small intestines in the conversion
of the aliment into nutriment.

[Illustration: Fig. LXIII.

1. Esophagus; 2. stomach; 3. liver raised, showing its under surface;
4. duodenum; 5. small intestines; 6. cæcum; 7. colon; 8. urinary
bladder; 9. gall bladder; 10. abdominal muscles divided and reflected.]

125. The organs which belong to the apparatus of excretion are—1. The
large intestines consisting of the cæcum (fig. LXIII. 6). 2. The colon
(fig. LXIII. 7). 3. The rectum (fig. LXIV. 10). It is the office of
these organs, which are called the large intestines, to carry out of
the system that portion of the alimentary mass which is not converted
into nourishment. 4. The kidneys (fig. LXIV. 6), the organs which
separate in the form of the urine an excrementitious matter from the
blood, in order that it may be conveyed out of the system.

[Illustration: Fig. LXIV.

General view of the viscera of the abdomen. 1. Stomach raised; 2. under
surface of liver; 3. gall bladder; 4. spleen; 5. pancreas; 6. kidneys;
7. ureters; 8. urinary bladder; 9. portion of the intestine called
duodenum; 10. portion of the intestine called rectum; 11. the aorta.]

126. The last division of the trunk, called the pelvis (fig. LXI. 3),
consists of a circle of large and firm bones, interposed between the
lower portion of the trunk and the inferior extremities (fig. XLV.).
The bones that compose the circle, distinct in the child, are firmly
united in the adult into a single piece; but as the original separation
between each remains manifest, they are always described as separate
bones. They are the sacrum (fig. XLV. 5), the coccyx (fig. XXXV.), the
ilium (fig. XLV. 11), the ischium (fig. XLV. 12), and the pubis (fig.
XLV. 13).

127. The sacrum, placed like a wedge between the moveable portion
of the spinal column and the lower extremities, forms the posterior
boundary of the pelvis. The figure of this bone is triangular (fig.
XLV. 5); its anterior surface is concave and smooth, for enlarging the
cavity of the pelvis and sustaining the organs contained in it (fig.
XLV. 5); its posterior surface is convex, irregular, and rough (fig.
XXXV.), giving origin to the great muscles that form the contour of the
hip, and to the strong muscles of the back and loins that raise the
spine and maintain the trunk of the body erect.

128. The base or upper part of the sacrum receives the last vertebra
of the loins on a large and broad surface (fig. XLV. 4), forming a
moveable joint; and the degree of motion at this point is greater than
it is at the higher points of the spinal column. Firmly united at its
sides with the haunch bones, it admits there of no degree of motion.

129. The coccyx, so named from its resemblance to the beak of the
cuckoo, when elongated by a succession of additional bones, forms the
tail in quadrupeds; but in man it is turned inwards to support the
parts contained in the pelvis, and to contract the lower opening of
the cavity. By means of a layer of cartilage, the medium by which this
bone is connected with the sacrum, it forms a moveable articulation,
continuing moveable in men until the age of twenty-five, and in women
until the age of forty-five; continuing moveable in women thus long, in
order that by yielding to the force which tends to push it backwards
during the period of labour, it may enlarge the lower aperture of the
pelvis, and so facilitate the process of parturition and diminish its
suffering.

130. The lateral boundaries of the pelvis are formed by the ilium,
the haunch bone (fig. XLV. 11), and by the ischium, the hip bone (fig.
XLV. 12). The ilium forms the lower part of the abdomen and the upper
part of the pelvis (fig. XLV. 11); its broad expanded wing supports the
contents of the abdomen, and gives attachment to the muscles that form
the anterior portion of its walls (figs. XLV. 11, and LXIII. 9); its
external convex surface sustains the powerful muscles that extend the
thigh; and along its internal surface is the prominent line which marks
the brim of the pelvis (fig. XLV. 15), and which divides this cavity
from that of the abdomen.

131. The ischium or hip bone is the lower part of the pelvis (fig.
XLV. 12); at its undermost portion is a rounded prominence called
the tuberosity (fig. XLV. 12), in its natural condition covered with
cartilage, upon which is superimposed a cushion of fat. It is this part
on which the body is supported in a sitting posture.

132. The pubis or share bone forms the upper and fore part of the
pelvis (fig. XLV. 13), and together with the two former bones,
completes the large and deep socket, termed the acetabulum (fig. XLV.
14), into which is received the head of the thigh-bone (fig. XXXIV.
4). The margin of the acetabulum and the greater part of its internal
surface is lined with cartilage, so that in its natural condition it is
much deeper than it appears to be when the bones alone remain.

133. The lower aperture of the pelvis, which appears large when all
the soft parts are removed, is not really large, for in its natural
state it is filled up partly by muscles and partly by ligaments, which
sustain and protect the pelvic organs, leaving only just space enough
for the passage to and from those which have their opening on the
external surface.

134. The cavity of the pelvis, together with all the organs contained
in it, are lined by a continuation of the membrane that invests the
abdomen and its contents.

135. The organs contained in the pelvis are the rectum (fig. LXIV. 9),
which is merely the termination of the large intestines, the urinary
bladder (fig. LXIV. 8), and the internal part of the apparatus of
reproduction.

136. The large and strong bones of the pelvis not only afford lodgment
and protection to the tender organs contained in its cavity, but
sustain the entire weight of the body, the trunk resting on the sacrum
as on a solid basis (fig. XLV. 5), and the lower extremities being
supported in the sockets in which the heads of the thigh-bones play, in
the varied movements of locomotion (fig. XXXIV. 4).

137. The last division of the body comprehends the superior and the
inferior extremities.

138. The superior extremities consist of the shoulder, arm, fore-arm,
and hand.

139. The soft parts of the SHOULDER are composed chiefly of muscles;
its bones are two, the scapula or the _blade bone_, and the clavicle or
the _collar bone_ (fig. LXV. 2, 4).

[Illustration: Fig. LXV.

1. Sternum; 2. clavicle; 3. ribs; 4. anterior surface of scapula; 5.
coracoid process of scapula; 6. acromion process of scapula; 7. margin
of glenoid cavity of scapula; 8. body of the humerus or bone of the
arm; 9. head of the humerus.]

140. The SCAPULA is placed upon the upper and back part of the thorax,
and occupies the space from the second to the seventh ribs (fig. LXV. 4)

[Illustration: Fig. LXVI.

1. Posterior surface of scapula; 2. margin of scapula; 3. acromion
process; 4. margin of glenoid cavity; 5. clavicle; 6. body of humerus;
7. head of humerus.]

Unlike that of any other bone of the body, it is embedded in muscles,
without being attached to any bone of the trunk, excepting at a single
point. From the bones of the thorax it is separated by a double layer
of muscles, on which it is placed as upon a cushion, and over the
smooth surface of which it glides. Originally, like the bones of the
skull, it consisted of two tables of compact bone, with an intermediate
layer of spongy bony substance (diploë); but, by the pressure of the
muscles that act upon it, it gradually grows thinner and thinner,
until, as age advances, it becomes in some parts quite transparent and
as thin as a sheet of paper.

141. The figure of the scapula is that of an irregular triangle (fig.
LXVI.). Its anterior surface is concave (fig. LXV. 4), corresponding to
the convexity of the ribs (fig. XLV. 7); its posterior surface is very
irregular (fig. LXVI. 1), being in some parts concave and in others
convex, giving origin especially to two large processes (figs. LXV. 5,
and LXVI. 3); one of which is termed the _acromion_ (fig. LXVI. 3),
and the other the _coracoid_ process of the scapula (fig. LXV. 5). The
margins of the bone, whatever the thinness of some portions of it, are
always comparatively thick and strong (fig. LXVI. 2), affording points
of origin or of insertion to powerful muscles. At what is called the
anterior angle of the bone there is a shallow oval depression covered
with cartilage and deepened by a cartilaginous margin, called the
_glenoid_ cavity of the scapula (figs. LXV. 7, and LXVI. 4), which
receives the head of the humerus or bone of the arm (figs. LXV. 9, and
LXVI. 7, 6).

142. The clavicle, the second bone of the shoulder, is a long and
slender bone, of the form of an italic [Illustration], projecting
a little forwards towards its middle, so as to give a slight convexity
of outline to the top of the chest and the bottom of the neck (fig.
LXV. 2). It is attached by one extremity to the sternum (fig. LXV. 2)
and by the other to the scapula (fig. LXV. 2), by moveable joints. The
nature of an immoveable joint has been explained (63). In the connexion
of the bones of the trunk, while the main object is to secure firmness
of attachment, some degree of motion is at the same time obtained (81
et seq.): but the mode in which the several bones of the extremities
are connected with each other and with the trunk, admits of so great a
degree of motion, that these articulations are pre-eminently entitled
to the name of moveable joints. The component parts of all moveable
joints are bone, cartilage, synovial membrane, and ligament. The great
character of a moveable joint is the approximation of two or more
bones; yet these bony surfaces are never in actual contact, but are
invariably separated from each other by cartilage. The cartilage either
covers the entire extent of the articulating surface of the bones,
as in the shoulder-joint, where both the head of the humerus and the
cavity of the scapula that receives it are enveloped in this substance
(fig. LXV. 7. 9), or a portion of it is placed between the articulating
surfaces of the bones, as in the joint between the clavicle and sternum
(fig. LXVII. _a_); which, when so placed, is termed an interarticular
cartilage (fig. LXVII. _a_). By its smooth surface cartilage lessens
friction; while by its elasticity it facilitates motion and prevents
concussion. Slightly organized cartilage is provided with comparatively
few blood-vessels and nerves. Had it been vascular and sensible like
the skin and the muscle, the force applied in the movements of the
joint would have stimulated the blood-vessels to inordinate action, and
the sensibility of the nerves would have been the source of constant
pain: every motion of every joint would have been productive of
suffering, and have laid the foundation of disease. The facility and
ease of motion obtained by the smoothness, elasticity, and comparative
insensibility of cartilage are still further promoted by the fluid
which lubricates it, termed synovia, secreted by a membrane called
synovial, which lines the internal surface of the joint, and which
bears a close resemblance to the serous (30). Synovia is a viscid
fluid of the consistence of albumen (5). It is to the joint what oil
is to the wheel, preventing abrasion and facilitating motion; but it
is formed by the joint itself, at the moment when needed, and in the
quantity required. The motion of the joint stimulates the synovial
membrane to secretion, and hence the greater the degree of motion, the
larger the quantity of lubricating fluid that is supplied. The several
parts of the apparatus of moveable joints are retained in their proper
position by ligamentous substance, which, as has been shown (96 and
97), is oftentimes so strong that it is easier to fracture the bone
than to tear the ligament, and in every case the kind and extent of
motion possessed by the joint are dependent mainly on the form of
the articulatory surfaces of the bones and on the disposition of the
ligaments.

143. In the joint formed by the clavicle and the sternum (fig. LXVII.
_a_) an interarticular cartilage is placed between the two bones which
are united, first by a strong fibrous ligament, which envelops them
as in a capsule (fig. LXVII. 1); by a second ligament, which extends
from the cartilage of the first rib to the clavicle (fig. LXVII. 4),
by which the attachment of the clavicle to the sternum is materially
strengthened; and by a third ligament which passes transversely from
the head of one clavicle to that of the other (fig. LXVII. 3). The
joint thus formed, though so strong and firm that the dislocation of
it is exceedingly rare, yet admits of some degree of motion in every
direction, upwards, downwards, forwards, and backwards; and this
articulation is the sole point by which the scapula is connected with
the trunk, and consequently by which the upper extremity can act, or be
acted upon, by the rest of the body.

[Illustration: Fig. LXVII.

1. The fibrous capsule of the sternum and clavicle; 2. the same laid
open, showing _a_, the interarticular cartilage; 3. the ligament
connecting the two clavicles; 4. the ligament joining the clavicle to
the first rib; 5. ligaments passing down in front of the sternum.]

144. The scapular extremity of the clavicle (fig. LXVIII. 6) is
attached to the processes of the scapula (fig. LXVIII. 4. 3) by several
ligaments of great strength (fig. LXVIII. 7, 8, 9). First by very
strong fasciculi which pass from the upper surface of the clavicle
to the acromion of the scapula (fig. LXVIII. 6); and secondly by two
ligaments which unite the clavicle with the coracoid process of the
scapula (fig. LXVIII. 8, 9). These ligaments are so powerful that they
resist a force capable of fracturing the clavicle; and they need to be
thus strong, for the clavicle is a shaft which sustains the scapula,
and through the scapula the whole of the upper extremity; and the main
object of the joint by which these bones are united, is to afford a
firm attachment of the scapula to its point of support.

[Illustration: Fig. LXVIII.

1. The clavicle; 2. the anterior part of the scapula; 3. the coracoid
process; 4. the acromion process; 5. the humerus; 6. ligaments binding
the scapular end of the clavicle to the acromion; 7. 8. 9. ligaments
passing from one process of the scapula to the other; 10. the fibrous
capsule of the shoulder-joint.]

145. The clavicle serves the following uses: it sustains the upper
extremity; it connects the upper extremity with the thorax; it prevents
the upper extremity from falling forwards upon the thorax; and it
affords a fixed point for steadying the extremity in the performance of
its various actions.

146. The glenoid cavity of the scapula (fig. LXV. 7) receives the head
of the humerus, the bone of the arm (fig. LXV. 9), and the two bones
being united by ligament form the shoulder-joint (fig. LXVIII.). This
joint is what is termed a ball and socket joint, the peculiarities
of which are two: first, beyond all others this mode of articulation
admits of free and extensive motion; in the present case, there is
the utmost freedom of motion in every direction, upwards, downwards,
backwards, and forwards. In the second place, this mode of articulation
admits of the motion of the limb without that of the body, or of the
motion of the body without that of the limb. When at rest, the arm may
be moved in almost any direction without disturbing the position of any
other part of the frame; the manifold advantages of which are obvious.
On the other hand, by careful management, very considerable variations
in the posture of the body may be effected without the communication
of any degree of motion to the limb; an unspeakable advantage when the
limb has sustained injury, or is suffering from disease.

147. It does not seem possible to construct a joint of great strength,
capable, at the same time, of the degree of motion possessed by the
joint of the shoulder. So shallow is the socket of the scapula, and
so large the head of the humerus, that it seems as if the slightest
movement must dislodge it from its cavity (fig. LXVI. 4. 7). For
sustaining heavy weights or resisting a great amount of pressure,
applied to it suddenly and in various directions, the arm is obviously
unfitted. But this is not its office. The superior extremities are the
organs of apprehension—the instruments by which the mind executes
the commands of the will. They do not need the strength required by
the organs that sustain the weight of the body and that perform the
function of locomotion; but they do need freedom and extent of motion:
to this strength may be sacrificed, and so it is; yet what can be
done to combine strength with mobility is effected. Large and strong
processes of bone, proceeding as has been shown (141), from the convex
surface of the scapula (figs. LXV. and LXVI.), overhang, and to a
considerable extent surround, the head of the arm-bone, especially
resisting the force that would dislodge it from its socket and drive
it upwards, inwards, and backwards (fig. LXV.), the directions in
which force is most commonly applied to it. By these processes of bone
the joint is greatly strengthened, especially in those directions.
Moreover, a strong ligament, termed the fibrous capsule (fig. LXVIII.
10) envelops the joint. This ligament, arising from the neck of
the scapula (fig. LXVIII. 10), expands itself in such a manner as
completely to surround the head of the humerus (fig. LXVIII. 10); and
then again contracts in order to be inserted into the neck of the bone
(fig. LXVIII. 10). This ligament is strengthened by the tendons of no
less than four muscles which are expanded over it, as well as by the
powerful substance termed fascia which is reflected upon it from both
the processes and ligaments of the scapula. In addition to all these
expedients for fortifying the joint, it receives a further security
in the position of the scapula, which is loose and unattached; which
slides easily over the ribs upon its cushion of flesh; which thus
obtains, by its facility of yielding, some compensation for its want of
strength, eluding the force which it cannot resist.

148. The arm consists of numerous and powerful muscles, and of a
single bone, the humerus, which belongs to the class of bones termed
cylindrical (185).

149. The upper end of the humerus terminates in a circular head
(fig. LXV. 9), which is received into the socket of the scapula (fig.
LXV. 9. 7) termed, as has been stated (141), its glenoid cavity. The
middle portion of the bone, or what is termed its shaft (fig. LXV. 8),
diminishes considerably in magnitude, and becomes somewhat rounded
(fig. LXV. 8), while its lower end again enlarges, and is spread out
into a flattened surface of great extent (fig. LXIX. 1, 3, 2, 4). Of
this broad flattened surface, the middle portion is grooved (fig. LXIX.
2): it is covered with cartilage; it forms the articulating surface
by which the arm is connected with the fore-arm. On each side of this
groove there is a projection of bone or tubercle, termed condyle (fig.
LXIX. 3, 4), the inner (fig. LXIX. 3) being much larger than the outer
(fig. LXIX. 4). The inner condyle gives origin to the muscles that
bend, the outer to those that extend the fore-arm and the fingers
(figs. LXXXIV. 1, 2, and LXXXV. 1).

[Illustration: Fig. LXIX.

1. Lower extremity of the humerus; 2. grooved surface; 3. internal
condyle; 4. external condyle; 5. the upper part of the ulna; 6. the
head; 7. the neck; 8. the tubercle of the radius.]

150. The muscles that act upon the arm arise from the back (fig.
LXXII. 2), the chest (fig. LXXI. 1), the clavicle (fig. LXXI. 1), and
the scapula (fig. LXXI. 3); and they move the arm with freedom and
power upwards, downwards, forwards, backwards, inwards, and outwards.
The chief muscle that raises the arm is the deltoid (fig. LXXI. 3),
which arises partly from the clavicle and partly from the scapula
(fig. LXXI. 3). It has the appearance of three muscles proceeding in
different directions, the different portions being separated by slight
fissures (figs. LXXI. 3, and LXXII. 3). The fibres converging unite
and form a powerful muscle which covers the joint of the humerus (fig.
LXXI. 3). It is implanted by a short and strong tendon into the middle
of the humerus (fig. LXXI. 4). Its manifest action is to pull the arm
directly upwards. Its action is assisted by the muscles that cover
the back of the scapula, which are in like manner inserted into the
humerus, and which, at the same time that they elevate the arm, support
it when raised.

[Illustration: Fig. LXXI.

View of the muscles on the fore part of the chest that act upon the
arm. 1. The muscle called the great pectoral; 2. the small pectoral; 3.
the deltoid; 4. the humerus.]

151. The principal muscle that carries the arm downwards is the
latissimus dorsi (fig. LXXII. 2), the broadest muscle of the body,
which, after having covered all the lower part of the back and loins,
terminates in a thin but strong tendon which stretches to the arm, and
is implanted into the humerus (fig. LXXII. 2), near the tendon of a
muscle immediately to be described,—the great pectoral. When the arm
is raised by the deltoid and its assistant muscles, the latissimus
dorsi carries it downwards with force, and its powerful action is
increased by that of other muscles which arise from the scapula and are
inserted into the arm.

152. The principal muscle that carries the arm forwards towards the
chest, is the great pectoral (fig. LXXI. 1), which, arising partly from
the clavicle (fig. LXXI. 1), partly from the sternum (fig. LXXI. 1),
and partly from the cartilages of the second, third, fourth, fifth, and
sixth ribs (fig. LXXI. 1), covers the greater part of the breast (fig.
LXXI. 1). Its fibres, converging, terminate in a strong tendon, which
is inserted near the tendon of the longissimus dorsi into the humerus,
about four inches below its head (fig. LXXI. 1). These two muscles form
the axilla or armpit, the anterior border of the axilla consisting of
the pectoral muscle. Though each of these muscles has its own peculiar
office, yet they often act in concert, thereby greatly increasing their
power, and the result of their combined action is to carry the arm
either directly downwards or to the side of the chest.

[Illustration: Fig. LXXII.

View of the muscles seated on the back part of the trunk that act
upon the shoulder and arm. 1. The muscle called the trapezius; 2. the
latissimus dorsi; 3. the deltoid.]

153. Some of the muscles that elevate the arm carry it inwards, and
others outwards; the muscles that carry it forwards likewise carry it
inwards; while of the muscles that pull it downwards, some direct it
forwards and inwards, and others backwards and outwards (151 and 152).

154. It has been already stated that the shoulder-joint is completely
surrounded by the muscular fibres or the tendinous expansions of
several of these powerful muscles, which have a far greater effect in
maintaining the head of the humerus in its socket than the fibrous
capsule of the joint; the latter being necessarily loose, in order
to allow of the extended and varied motions of the arm, whereas the
muscles that encompass the joint adhere closely and firmly to it.
Moreover, by virtue of their vital power these muscles act with an
efficiency which a mere ligamentous band is incapable of exerting; for
they apportion the strength of resistance to the separating force, and
react with an energy proportioned to the violence applied.

155. The bones of the fore-arm are two, the ulna and the radius (figs.
LXIX. and LXXIII.). The ulna is essentially the bone of the elbow
(figs. LXIX. 5, and LXXIII. 3); the radius that of the hand (fig.
LXXV.). Supposing the arm to hang by the side of the body, and the palm
of the hand to be turned forwards, the ulna, in apposition with the
little finger, occupies the inner; and the radius, in apposition with
the thumb, occupies the outer part of the fore-arm (fig. XXXIV. 3).

[Illustration: Fig. LXXIII.

  1. The internal condyle of the humerus; 2. the external
  condyle of the humerus; 3. the olecranon process of the ulna;
  4. the head of the radius.]

156. The upper end of the ulna belonging to the elbow is large (figs.
LXIX. 5, and LXXIII. 3). It sends backwards the large projection
commonly named the elbow or _olecranon_ (fig. LXXII. 3), in the centre
of which there is a smooth and somewhat triangular surface (fig.
LXXIII. 3) which is always covered by skin of a coarse texture, like
that placed over the lower part of the knee-pan, as if nature intended
this for a part on which we may occasionally lean and rest. Large at
the elbow, the ulna gradually grows smaller and smaller as it descends
towards the wrist, where it ends in a small round head (fig. LXXXII.
2), beyond which, on the inner side, or that corresponding to the
little finger, it projects downwards a small rounded point, termed
the styloid process (fig. LXXXII. 3). As the styloid process and the
olecranon, the two extremities of the ulna (figs. LXXIII. 3, and
LXXII. 3), are easily and distinctly felt, the length of this bone was
primitively used as a measure, called a cubit, which was the ancient
name of the bone.

157. The radius, the second bone of the fore-arm, placed along its
outer part next the thumb, is small at its upper end (figs. LXIX. 6,
and LXXIII. 4); but its body is larger than that of the ulna; while its
lower end, next the wrist to which it properly belongs, is very bulky
(fig. LXXXII. 1). Its upper end is formed into a small circular head,
which is united by distinct joints both to the humerus and to the ulna
(fig. LXIX. 6). The top of its rounded head is excavated into a shallow
cup (figs. LXIX. 6, and LXXIII. 4) which receives a corresponding
convexity of the humerus (fig. LXIX. 2), and its lower extremity is
excavated into an oblong cavity, which receives two of the bones of the
wrist (fig. LXXXIII. 1. 4).

158. The joint of the elbow is composed above of the condyles of the
humerus (fig. LXIX. 3. 2), and below by the heads of the ulna and
radius (fig. LXIX. 5. 6).

159. The upper surface of the ulna is so accurately adapted to the
lower surface of the humerus that the one seems to be moulded on
the other (figs. LXIX. 5, and LXXIII. 3), and the form of these
corresponding surfaces, which are everywhere covered with cartilage,
is such as to admit of free motion backwards and forwards, that is,
of extension and flexion; but to prevent any degree of motion in any
other direction. The joint is therefore a hinge-joint, of which the two
motions of flexion and extension are the proper motions. This hinge is
formed on the part of the humerus by a grooved surface, with lateral
projections (fig. LXIX. 2, 3, 4), and on the part of the ulna by a
middle projection with lateral depressions (fig. LXIX. 5): the middle
projection of the ulna turning readily on the grooved surface of the
humerus (fig. LXIX. 2).

160. The bones are held in their proper situation, first, by a
ligament on the fore part of the arm, called the anterior (fig. LXXIV.
6), which arises from the lower extremity of the humerus, and is
inserted into the upper part of the ulna and the coronary ligament of
the radius (fig. LXXIV. 6. 8); secondly, by another ligament on the
back part of the arm, called the posterior ligament (fig. LXXV. 8),
placed in the cavity of the humerus that receives the olecranon of the
ulna (fig. LXXV. 8); and thirdly, by two other ligaments at the sides
of the ulna (fig. LXXV. 6, 7). The ulna and radius are united, first,
by a ligament called the coronary, which, arising from the ulna, passes
completely around the head of the radius (fig. LXXVI. 3), and the
attachment of which, while sufficiently close to prevent the separation
of the two bones, is yet not adherent to the radius, for a reason
immediately to be assigned; secondly, by another ligament which passes
in an oblique direction from one bone to the other (fig. LXXVI. 4);
and thirdly, by a dense and broad ligament, termed the _interosseous_
(figs. LXXIV. 10, and LXXVI. 5), which fills up the space between the
two bones nearly in their whole extent. This ligament serves other
offices besides that of forming a bond of union, affording, more
especially, a greater extent of surface for the attachment of muscles,
and separating the muscles on the anterior from those on the posterior
part of the limb.

[Illustration: Fig. LXXIV.

  Anterior view of the ligaments of the elbow-joint. 1. The
  lower portion of the humerus; 2. the upper portion of the
  radius; 3. the upper portion of the ulna; 4. the internal
  condyle; 5. the external condyle; 6. the anterior ligament;
  7. portion of the internal lateral ligament; 8. portion of
  the coronary ligament; 9. the oblique ligament; 10. upper
  portion of the interosseous ligament.]

[Illustration: Fig. LXXV.

  Posterior view of the ligaments of the elbow-joint. 1. Lower
  end of the humerus; 2. internal condyle; 3. external condyle;
  4. the olecranon process of the ulna; 5. the upper portion of
  the radius; 6. the internal lateral ligament; 7. the external
  lateral ligament; 8. the posterior ligament.]

[Illustration: Fig. LXXVI.

View of the ligaments connecting the ulna and radius at their upper
part. 1. The radius; 2. the ulna; 3. the coronary ligament surrounding
the head of the radius; 4. the oblique ligament passing from the ulna
to the tubercle of the radius; 5 the upper portion of the interosseous
ligament.]

161. At their inferior extremities the ulna and radius are united
partly by the interosseous ligament (fig. LXXVII. 1) and partly by
ligamentous fibres which pass transversely from one bone to the other
(fig. LXXVII. 2) on the anterior and the posterior surface of the
fore-arm.

[Illustration: Fig. LXXVII.

1. Interosseous ligament; 2. transverse fibres passing between the
radius and ulna, and uniting the two bones; 3. 4. 5. posterior and
lateral ligaments of the wrist joint; 6. ligaments uniting the bones of
the wrist with one another; 7. 8. ligaments which attach the metacarpal
to the carpal bones; 9. transverse ligaments for the attachment of the
phalanges of the fingers; 10. lateral ligaments for the attachment of
the phalanges of the fingers 11. ligaments of the thumb.]

162. The lower extremity of the radius is also united to the wrist;
and the hand being attached to the wrist, the junction of the hand and
the fore-arm is effected by the articulation of the wrist with the
radius (fig. LXXVII.). The ligaments which connect the bones of the
wrist with the radius are bands of exceeding strength (fig. LXXVII. 3).

163. The muscles that act upon the fore-arm are placed upon the arm
(fig. LXXVIII.). The joint of the elbow being a hinge-joint, the
fore-arm can admit only of two motions, namely, flexion and extension.
The muscles by which these motions are effected are four, two for each;
the two flexors being placed on the fore part (fig. LXXVIII. 2. 4), and
the two extensors on the back part of the arm (fig. LXXIX. 5).

164. The two flexor muscles of the fore-arm are termed the biceps and
the brachialis (fig. LXXVIII. 2, 4). The biceps is so called because
it has two distinct heads or points of origin (fig. LXXVIII. 2), both
of which arise from the scapula (fig. LXXVIII. 2). About a third part
down the humerus the two heads meet, unite and form a bulky muscle
(fig. LXXVIII. 2), which, when it contracts, may be felt like a firm
ball on the fore part of the arm, the upper part of the ball marking
the point of union of the two heads (fig. LXXVIII. 2). The muscle
gradually becoming smaller, at length terminates in a rounded tendon
(fig. LXXVIII. 3), which is implanted into the tubercle of the radius
a little below its neck (fig. LXXVIII. 3). It is an exceedingly thick
and powerful muscle, and its manifest action is to bend the fore-arm
with great strength. But since its tendon is inserted into the radius,
besides bending the fore-arm, it assists other muscles that also act
upon the radius in the performance of a function to be described
immediately (168).

[Illustration: Fig. LXXVIII.

View of the flexor muscles of the fore-arm. 1. The anterior surface
of the scapula; 2. the muscle called biceps; 3. tendon of the biceps
passing to the tubercle of the radius; 4. the muscle called brachialis.]

165. The second flexor of the fore-arm, termed the brachialis, is
placed immediately under the biceps, and is concealed by it for a
considerable part of its course (fig. LXXVIII. 4). Arising from the
humerus, on each side of the insertion of the deltoid, it continues its
attachment to the bone all the way down the fore part of the humerus,
to within inch of the joint; it then passes over the joint, adhering
firmly to the anterior ligament (fig. LXXVIII. 4), and is inserted by a
strong tendon into the ulna (fig. LXXVIII. 4). It is a thick and fleshy
muscle, powerfully assisting the action of the biceps.

166. The two extensor muscles are named the triceps and the anconeous
(fig. LXXIX.). The triceps, seated on the back part of the arm, derives
its name from having three distinct points of origin, or three separate
heads (fig. LXXIX. 5); one of which arises from the scapula and two
from the humerus (fig. LXXIX. 5). All these heads adhere firmly to the
humerus, as the brachialis does on the fore part of the arm, down to
within an inch of the joint (fig. LXXIX. 5), where they form a strong
tendon, which is implanted into the olecranon of the ulna (fig. LXXIX.
3); the projection of which affords a lever for increasing the action
of the muscle. In all animals that leap and bound, this process of the
ulna is increased in length in proportion to their power of performing
these movements. The triceps forms an exceedingly thick and strong
muscle, which envelops the whole of the back part of the arm (fig.
LXXIX.); its action is simple and obvious; it powerfully extends the
fore-arm. The anconeous, a small muscle of a triangular form, arising
from the external condyle of the humerus, and inserted into the ulna a
little below the olecranon, assists the action of the triceps.

[Illustration: Fig. LXXIX.

View of the extensor muscles of the fore-arm. 1. The scapula; 2. the
upper part of the humerus; 3. upper end of the ulna; 4. upper end
of the radius; 5. the muscle called _triceps_, the extensor of the
fore-arm.]

167. Such are the motive powers which act upon the fore-arm, and
which produce all the motions of which the hinge-joint of the elbow
renders it capable. But besides flexion and extension, the fore-arm is
capable of the motion of rotation, which is accomplished by means of
the radius. It has been shown (157) that the top of the rounded head of
the radius is excavated into a shallow cup (figs. LXIX. 6, and LXXIII.
4) which receives a corresponding convexity of the humerus (figs.
LXIX. 2, and LXXIII. 2). In consequence of this articulation with the
humerus, the radius, like the ulna, can move backwards and forwards
in flexion and extension, the proper movements of the hinge-joint;
but that portion of the margin of the hinge of the radius which is in
apposition with the ulna is convex (fig. LXIX. 6), and is received into
a semilunar cavity hollowed out in the ulna (fig. LXIX. 5). In this
cavity the rounded head of the radius revolves, the two bones being
held together by the ligament already described (160), which surrounds
the head of the radius (fig. LXXVI. 3), and which holds it firmly
without being adherent to it, and without impeding in any degree the
rotatory motion of the radius. Below, the surface of the radius next
the ulna is hollowed out into a semilunar cavity (fig. LXXXII. 1),
which receives a corresponding convex surface of the ulna (fig. LXXXII.
2), upon which convex surface the radius rolls (fig. LXXXII. 1). Thus,
by the mode in which it is articulated with the ulna above, the radius
turns upon its own axis. By the mode in which it is articulated with
the ulna below, the radius revolves upon the head of the ulna; and, in
consequence of both articulations, is capable of performing the motion
of rotation. Moreover, the hand being attached to the radius through
the medium of the wrist (figs. LXXXII. 1. 4. and LXXXIII. 1. 4) must
necessarily follow every movement of the radius; the rotation of which
brings the hand into two opposite positions. In the one, the palm of
the hand is directed upwards (fig. LXXXII.); in the other, it is turned
downwards (fig. LXXXIII.). When the hand is turned upwards, it is said
to be in the state of _supination_ (fig. LXXXII.); when downwards, in
that of _pronation_ (fig. LXXXIII.). A distinct apparatus of muscles
is provided for effecting the rotation of the radius, in order to
bring the hand into these opposite states: one set for producing its
supination, and another its pronation.

168. The principal supinators arise from the external condyle of the
humerus (fig. LXXX.), and are called long and short (fig. LXXX. 4, 5).
The long supinator extends as far as the lower end of the radius, into
which it is inserted (fig. LXXX. 4): the short supinator surrounds the
upper part of the radius, and is attached to it in this situation (fig.
LXXX. 5.). Moreover, the triceps, being inserted into the radius (164),
often cooperates with the supinators and powerfully assists their
action.

169. The principal pronators are also two, called the round and the
square (figs. LXXXI. and LXXXVI. 1). The round pronator arises from the
internal condyle, and passing downwards, is inserted into the middle
of the radius (fig. LXXXI. 4); the square pronator is a small muscle
between the radius and ulna, at their lower extremities being attached
to each (fig. LXXXVI. 1).

[Illustration: Fig. LXXX.

View of the supinators of the radius and hand. 1. The humerus; 2. the
ulna; 3. the radius; 4. the muscle called the long supinator passing to
be inserted into the lower portion of the radius; 5. the muscle, called
the short supinator, surrounding the upper part of the radius.]

170. The action of these muscles in producing the rotation of the
radius, and so rendering the hand supine or prone, is sufficiently
manifest from the mere inspection of the diagrams (fig. LXXXI. 4).

[Illustration: Fig. LXXXI.

View of the pronators of the hand. 1. Lower end of the humerus; 2. the
radius; 3. the ulna; 4. the muscle called the round _pronator_, one of
the powerful pronators of the hand.]

171. The hand is composed of the carpus, metacarpus, and fingers.

172. The carpus (fig. LXXXII. 4) consists of eight small wedge-shaped
bones, placed in a double row, each row containing an equal number, and
the whole disposed like stones in an arch (fig. LXXXII. 4). They do in
fact form an arch, the convexity of which is upwards, on the dorsal
surface (fig. LXXXIII. 4); and the concavity downwards, on the palmar
surface (fig. LXXXII. 4). But they differ from the stones of an arch
in this, that each bone is joined to its fellow by a distinct moveable
joint, each being covered with a smooth articulating cartilage. At the
same time all of them are tied together by ligaments of prodigious
strength, which cross each other in every direction (fig. LXXVII. 6),
so that the several separate joints are consolidated into one great
joint. The consequence of this mechanism is that some degree of motion
is capable of taking place between the several bones, which, when
multiplied together, gives to the two rows of bones such an extent of
motion, that when the wrist is bent the arch of the carpus forms a kind
of knuckle. By this construction a facility and ease of motion, and
a power of accommodation to motion and force, are obtained, such as
belong to no arch contrived by human ingenuity.

[Illustration: Fig. LXXXII.

1. Lower extremity of the radius; 2. lower extremity of the ulna;
3. styloid process of the ulna; 4. bones of the carpus or wrist;
5. metacarpal bones; 6. first phalanges of the fingers; 7. second
phalanges of the fingers; 8. third phalanges of the fingers.]

173. The metacarpus (fig. LXXXII. 5), the middle portion of the hand,
interposed between the wrist and the fingers, is composed of five
bones, which are placed parallel to each other (fig. LXXXII. 5). They
are convex outwardly, forming the back (fig. LXXXIII. 5), and concave
inwardly, forming the hollow of the hand (fig. LXXXII. 5). They are
large at each end, to form the joints by which they are connected with
the wrist and fingers (figs. LXXXII. and LXXXIII.): they are small in
the middle, in order to afford room for the lodgment and arrangement
of the muscles, that move the fingers from side to side (fig. LXXXVI.
2). Their ends, which are joined to the carpus, are connected by nearly
plane surfaces (figs. LXXXII. and LXXXIII.): their ends, which support
the fingers, are formed into rounded heads, which are received into
corresponding cup-shaped cavities, excavated in the top of the first
bones of the fingers (fig. LXXXII. 5.). The powerful ligaments that
unite these bones pass, both on the dorsal and the palmar surface, from
the inferior extremity of the second row of the carpal to the bases of
the metacarpal bones (fig. LXXVII, 7, 8). The ligaments are arranged in
such a manner as to limit the motions of the joints chiefly to those
of flexion and extension, allowing, however, a slight degree of motion
from side to side.

174. Each of the fingers is composed of three separate pieces of bone,
called phalanges; the thumb has only two (fig. LXXXII. 6, 7, 8): the
phalanges are convex outwardly (fig. LXXXII. 6, 7, 8) for increasing
their strength, and flattened inwardly (fig. LXXXIII. 6, 7, 8) for
the convenience of grasping. The last bones of the fingers, which are
small, terminate at their under ends, in a somewhat rounded and rough
surface (fig. LXXXIII. 8), on which rests the vascular, pulpy, and
nervous substance, constituting the special organ of touch, placed at
the points of the fingers, and guarded on the upper surface by the nail
(fig. LXXXII. 8).

[Illustration: Fig. LXXXIII.

1. Lower extremity of the radius; 2. lower extremity of the ulna; 3.
styloid process of the ulna; 4. bones of the carpus; 5. metacarpal
bones; 6. 7. 8. first, second, and third phalanges of the fingers.]

175. The round inferior extremity of the metacarpus is admitted into
the cavity of the superior extremity of the first phalanx of the five
fingers (figs. LXXXII. and LXXXIII.), and their joints are connected by
lateral and transverse ligaments of great strength (fig. LXXVII. 9).
The situation and direction of the ligaments which unite the several
phalanges of the fingers (fig. LXXVII. 9) are precisely the same as
those of the articulation of the phalanges with the metacarpus (fig.
LXXVII. 7, 8); and the articulation of these bones with one another is
such as to admit only of the motions of flexion and extension.

176. The muscles which perform these motions are seated for the most
part on the fore-arm. Independently of the supinators and pronators
which have been already described (167 et seq.), there are distinct
sets of muscles for bending and extending the wrist and the fingers.
The flexors arise from the internal, and the extensors from the
external, condyle of the humerus (fig. LXIX. 3, 4). The internal
condyle is larger and longer than the external (fig. LXIX. 3, 4); for
the flexors require a larger point of origin and a longer fulcrum
than the extensor muscles; because to the actions of flexion, such as
grasping, bending, pulling, more power is necessary than to the action
of extension, which consists merely in the unfolding or the opening of
the hand previously to the renewal of the grasp.

177. For the same reason, two muscles are provided for flexing,
while only one is provided for extending the fingers. The flexors,
bulky, thick, and strong, are placed on the fore part of the fore-arm
(fig. LXXXIV.). The first, named the superficial flexor (fig. LXXXIV.
1), about the middle of the arm, divides into four fleshy portions,
each of which ends in a slender tendon (fig. LXXXIV. 1). As these
tendons approach the fingers they expand (fig. LXXXIV. 1), and when
in apposition with the first phalanx, split and form distinct sheaths
for the reception of the tendons of the second flexor (fig. LXXXIV.
3). After completing the sheath, the tendons proceed forward along the
second phalanx, into the fore part of which they are implanted, and
the chief office of this powerful muscle is to bend the second joint
of the fingers upon the first, and the first upon the metacarpal bone.
Its action is assisted by a second muscle, called the deep or profound
flexor (fig. LXXXIV. 2), because it lies beneath the former; or the
perforans, because it pierces it. Bulky and fleshy, this second flexor,
like the first, about the middle of the arm, divides into four tendons,
which, entering the sheaths prepared for them in the former muscle
(where the tendons are small and rounded for their easy transmission
and play), pass to the root of the third phalanx of the fingers into
which they are implanted (fig. LXXXIV. 3).

[Illustration: Fig. LXXXIV.

View of the flexor muscles of the fingers. 1. The superficial flexor,
divided and turned aside, to show, 2. the deep flexor; 3. sheaths for
the tendons of the deep flexor, formed by the splitting of the tendons
of the superficial flexor; 4. the anterior annular ligament, divided
and turned aside.]

118. The muscle that extends the fingers, called the common extensor,
is placed on the back part of the fore-arm (fig. LXXXV.), about the
middle of which it divides into four portions which terminate in
so many tendons (fig. LXXXV. 2). When they reach the back of the
metacarpal bones, these tendons become broad and flat, and send
tendinous expansions to each other, forming a strong tendinous sheath
which surrounds the back of the fingers (fig. LXXXV. 2). These
tendinous expansions are inserted into the posterior part of the bones
of the four fingers (fig. LXXXV. 2); and their office is powerfully to
extend all the joints of all the fingers (fig. LXXXV. 2).

179. On both the palmar and dorsal regions of the wrist are placed
ligaments for tying down these tendons, and preventing them from
starting from their situation during the action of the muscles (figs.
LXXXIV. and LXXXV.). On the palmar region an exceedingly strong
ligament passes anteriorly to the concave arch of the carpus (fig.
LXXXIV. 4) for the purpose of tying down the tendons of the flexor
muscles. On the dorsal surface (fig. LXXXV.), a similar ligament,
passing in an oblique direction from the styloid process of the radius
to the styloid process of the ulna (fig. LXXXV. 3), performs the same
office in tying down the tendons of the extensor muscle. Both these
ligaments are called annular.

[Illustration: Fig. LXXXV.

View of the extensor muscles of the fingers. 1. The common extensor,
sending (2 2 2 2) tendons to each finger; 3. the posterior annular
ligament.]

180. In the palm of the hand are placed additional muscles which
assist the flexors of the fingers (fig. LXXXVI. 2), being chiefly
useful in enabling the fingers to perform with strength and precision
short and quick motions. There are especially four small and rounded
muscles (fig. LXXXVI. 2), resembling the earth worm in form and size,
and hence called lumbricales; but as their chief use is to assist the
fingers in executing short and rapid motions, they have also received
the better name of the musculi fidicinales.

[Illustration: Fig. LXXXVI.

1. The muscle called the square pronator; 2. muscles seated in the palm
of the hand, by which, chiefly, the fingers execute short and rapid
motions.]

181. The thumb, in consequence of the comparative looseness of its
ligaments, is capable of a much greater extent of motion than the
fingers, and can be applied to any part of each of the fingers, to
different parts of the hand, and in direct opposition to the power
exerted by the whole of the fingers and hand, in the act of grasping.
The muscles which enable it to perform these varied motions, and which
act powerfully in almost every thing we do with the hand, form a mass
of flesh at the ball of the thumb (fig. LXXXVII. 1), almost entirely
surrounding it. The little finger is also provided with a distinct
apparatus of muscles (fig. LXXXVII. 2), which surrounds its root, just
as those of the thumb surround its ball, in order to keep it firm in
opposition to the power of the thumb in the act of grasping, and in
various other motions.

[Illustration: Fig. LXXXVII.

1. The mass of muscles forming the ball of the thumb; 2. the mass of
muscles forming the ball of the little finger; 3. tendons of one of the
flexor muscles of the fingers; 4. sheaths formed by the tendons of the
superficial flexor for the reception of the tendons of the deep flexor.]

182. The upper extremity is covered by a tendinous expansion or fascia
which envelopes the whole arm, encloses its muscles as in a sheath,
and affords them, in their strong actions, "that kind of support which
workmen feel in binding their arms with thongs." This fascia likewise
descends between many of the muscles, forming strong partitions between
them, and affording points of origin to many of their fibres, scarcely
less fixed than bone itself.

183. From the whole, it appears, that the first joint of the upper
extremities, that of the shoulder, is a ball and socket joint, a joint
admitting of motion in every direction; that the second joint, that of
the elbow, is partly a hinge-joint, admitting of flexion and extension,
and partly a rotation joint, admitting of a turning or rotatory motion;
and that the joints of the wrist and of the fingers are likewise
hinge-joints, admitting at the same time of some degree of lateral
motion. When these various motions are combined, the result is that
the hand can apply itself to bodies in almost every direction, in any
part of the area described by the arm, when all the joints are moved to
their utmost extent. There is thus formed an instrument of considerable
strength, capable of a surprising variety and complexity of movements,
capable of seizing, holding, pulling, pushing and striking with great
power, yet at the same time capable of apprehending the minutest
objects, and of guiding them with the utmost gentleness, precision, and
accuracy, so that there are few conceptions of the designing mind which
cannot be executed by the skilful hand.

184. The lower extremities consist of the thigh, leg, and foot.

185. The osseous part of the thigh consists of a single bone, called
the femur (fig. XXXIV. 4), the longest, thickest, and strongest bone in
the body. It sustains the entire weight of the trunk, and occasionally
much heavier loads superimposed upon it. It is constructed in such
a manner as to combine strength with lightness. This is effected by
rendering the bone what is technically called cylindrical; that is, a
bone in which the osseous fibres are arranged around a hollow cylinder.
There are two varieties of osseous matter,—the compact, in which the
fibres are dense and solid (fig. LXXXVIII. 1), and the spongy, in which
the fibres are comparatively tender and delicate (fig. LXXXVIII. 2).
Both varieties are, indeed, combined, more or less, in every bone,
the compact substance being always external, and the spongy internal;
but in the cylindrical bones the arrangement is peculiar. Every long
or cylindrical bone consists of a body or shaft (fig. LXXXVIII. 4.),
and of two extremities (fig. LXXXVIII. 5). The body is composed
principally of compact substance, which on the external surface is so
dense and solid, that scarcely any distinct arrangement is visible;
but towards the interior this density diminishes; the fibres become
distinct (fig. LXXXVIII. 5), and form an expanded tissue of a cellular
appearance (fig. LXXXVIII. 5), the cells being called cancelli, and
the structure cancellated. In the centre of the bone even the cancelli
disappear; the osseous fibres terminate; and a hollow space is left
filled up, in the natural state, by an infinite number of minute
membranous bags which contain the marrow (fig. LXXXVIII. 3). In the
body of the bone, to which strength is requisite, that part being the
most exposed to external violence, the compact matter is arranged
around a central cavity. By this means strength is secured without
any addition of weight; for the resisting power of a cylindrical body
increases in proportion to its diameter; consequently the same number
of osseous fibres placed around the circumference of a circle produce
a stronger bone than could have been constructed had the fibres been
consolidated in the centre, and had the diameter been proportionally
diminished. The hollow space thus gained in its centre, renders the
bone lighter by the subtraction of the weight of as many fibres as
would have gone to fill up that space; while its strength is not only
not diminished by this arrangement, but positively increased. On the
other hand, at the extremities of the bone, space, not strength, is
required; required for the attachment and arrangement of the tendons
of the muscles that act upon it, and for the formation of joints (fig.
LXXXVIII. 5). Accordingly, at its extremities the bone swells out into
bulky surfaces; but these surfaces are composed, not of dense and solid
substance, but of spongy tissue, covered by an exceedingly thin crust
of compact matter, and so, as by the former expedient strength is
secured without increase of weight, by this, space is obtained without
increase of weight.

[Illustration: Fig. LXXXVIII.

A section of the femur, showing, 1. the compact bony substance; 2. the
spongy or cancellated structure; 3. the internal cavity containing the
marrow; 4. body; 5, extremities of the bone.]

186. The thigh-bone, placed at the under and outer part of the pelvis,
has an oblique direction, the under being considerably nearer its
fellow than the upper end (fig. XXXIV. 4), in order to afford space for
the passages at the bottom of the pelvis, and also to favour the action
of walking. The body of the bone, which is of a rounded form (fig.
XXXIV. 4), is smooth on its anterior surface (fig. XXXIV. 4), where it
is always slightly convex, the convexity being forwards (fig. XXXIV.
4), while its posterior surface is irregular and rough, and forms a
sharp prominent line, termed the linea aspera (fig. XXXV. 4), giving
attachment to numerous muscles.

187. The superior extremity of the femur terminates in a large ball or
head, which forms nearly two-thirds of a sphere (fig. LXXXIX. 4.). It
is smooth, covered with cartilage, and received into the socket of the
ilium called the acetabulum, which, deep as it is, is still further
deepened by the cartilage which borders the brim (fig. LXXXIX. 3). The
brim is particularly high in the upper and outer part, because it is in
this direction that the reaction of the ground against the descending
weight of the trunk tends to dislodge the ball from its socket.

188. Passing obliquely downwards and outwards from the ball, is that
part of the femur which is called the neck (fig. LXXXIX. 5). It spreads
out archlike between the head and the body of the bone, and is more
than an inch in length (fig. LXXXIX. 5). It is thus long in order
that the head of the bone may be set deep in its socket, and that its
motions may be wide, free, and unembarrassed.

[Illustration: Fig. LXXXIX.

1. Lower portion of the ilium; 2. tuberosity of the ischium: 3. socket
for the head of the femur, or thigh-bone; 4. head of the femur; 5. neck
of the femur; 6. the great process of the femur called the trochanter
major; 7. the body of the femur.]

189. From the external surface of the femur, nearly in a line with
its axis, proceeds the largest and strongest bony process of the body
which gives insertion to its most powerful muscles, namely, those that
extend the thigh and that turn it upon its axis (fig. LXXXIX. 6).
Because, from its oblique direction, it rotates the thigh, this process
is called the trochanter, and, from its size, the trochanter major. At
the under and inner part of the neck on the posterior surface of the
bone, is a similar process, but much smaller, called the trochanter
minor (fig. XXXV. 4), into which are inserted the muscles that bend the
thigh.

190. The inferior extremity of the femur, much broader and thicker
than the superior (fig. XC. 1), is terminated by two eminences, with
smooth surfaces, termed condyles (fig. XC. 2), which, articulated with
the tibia, and the patella, form the joint of the knee (figs. XC. 2, 4,
5, and XCI. 1, 2, 3).

[Illustration: Fig. XC.

1. Lower end of the femur; 2. condyles of the femur; 3. upper end of
the tibia; 4. articular surfaces on the head of the tibia on which the
thigh-bone plays; 5. the patella, or knee-pan; 6. upper end of the
fibula, not entering into the knee-joint.]

[Illustration: Fig. XCI.

Posterior view of the bones forming the knee-joint. 1. Lower end of the
femur; 2. upper end of the tibia; 3. articular surfaces on the head of
the tibia, on which the thigh-bone plays; 4. upper end of the fibula,
not entering into the knee joint.]

191. The bones of the leg, two in number, consist of the tibia (fig.
XC. 3) and fibula (fig. XC. 6). The tibia, next to the femur, the
longest bone in the body, is situated at the inner side of the leg
(fig. XC. 3). Its superior extremity is bulky and thick (fig. XC. 3).
The top of it forms two smooth and slightly concave surfaces, adapted
to the convex surfaces of the condyles of the femur (fig. XC. 4, 2).
On its outer side there is a smooth surface, to which the head of the
fibula is attached (fig. XC. 6). Its lower extremity, which is small,
forms a concavity adapted to the convexity of the bone of the tarsus,
called the astragalus, with which it is articulated (fig. XCII. 4.)
Its inner part is produced so as to form the inner ankle (figs. XCII.
2, and XCIII. 3): its outer side is excavated into a semilunar cavity,
for receiving the under end of the fibula, which forms the outer ankle
(figs. XCII. 3, and XCIII. 4).

192. The fibula, in proportion to its length the most slender bone of
the body, is situated at the outer side of the tibia (fig. XC. 6). Its
upper end formed into a head, with a flat surface on its inner side
(figs. XC. 6, and XCI. 4), is firmly united to the tibia (fig. XC. 4).
Its lower end forms the outer ankle, which is lower and farther back
than the inner (fig. XCII. 3, 2).

[Illustration: Fig. XCII.

Anterior view of the bones forming the ankle-joint. 1. Lower end of
the tibia; 2. production of the tibia, forming the inner ankle; 3.
lower end of the fibula, forming the outer ankle; 4. upper part of the
astragalus: these three bones form the ankle-joint; 5 5 5, other bones
of the tarsus; 6 6 6 6 6 metatarsal bones.]

[Illustration: Fig. XCIII.

Posterior view of the bones forming the ankle-joint. 1. Lower end of
the tibia; 2. lower end of the fibula; 3. internal malleolus or ankle;
4. external malleolus or ankle; 5. one of the tarsal bones, called the
astragalus, with which the tibia and fibula are articulated; 6. the os
calcis or heel.]

193. The patella, or knee-pan (fig. XC. 5), is a light but strong
bone, of the figure of the heart as painted on playing-cards, placed
at the fore part of the joint of the knee, and attached by a strong
ligament to the tibia, the motions of which it follows (fig. XC. 5). It
is lodged, when the knee is extended, in a cavity formed for it in the
femur (fig. XC.); when bent, in a cavity formed for it at the fore part
of the knee (fig. XC. 5).

194. The foot consists of the tarsus, metatarsus, and toes.

195. The tarsus, or instep, is composed of seven strong,
irregular-shaped bones, disposed like those of the carpus, in a double
row (fig. XCII. 4, 5). The arrangement of the tarsal bones is such as
to form an arch, the convexity of which above, constitutes the upper
surface of the instep (fig. XCII. 4, 5): in the concavity below are
lodged the muscles, vessels, and nerves that belong to the sole.

196. The metatarsus consists of five bones, which are placed parallel
to each other (fig. XCII. 6), and which extend between the tarsus
and the proper bones of the toes (fig. XCII. 6). Their extremities,
especially next the tarsus, are large, in order that they may form
secure articulations with the tarsal bones (fig. XCII. 6). Their
bodies are arched upwards (fig. XCII. 6), slightly concave below, and
terminate forwards in small, neat, round heads, which receive the
first bones of the toes, and with which they form joints, admitting
of a much greater degree of rotation than is ever actually exercised,
in consequence of the practice of wearing shoes. The natural, free,
wide-spreading form of the toes, and the consequent security with
which they grasp the ground, is greatly impaired by this custom. Taken
together, the bones of the metatarsus form a second arch corresponding
to that of the tarsus (fig. XCVIII. 2).

197. Each toe consists of three distinct bones, called, like those
of the fingers, phalanges (fig. XCVIII.), but the great toe, like
the thumb, has only two (fig. XCVIII.). That extremity of the first
phalanges which is next the metatarsal bones is hollowed into a socket
for the head of the metatarsal bones.

198. Besides the bones already described, there are other small bones,
of the size and figure of flattened peas, found in certain parts of
the extremities, never in the trunk, called sesamoid, from their
resemblance to the seed of the sesamum. They belong rather to the
tendons of the muscles than to the bones of the skeleton. They are
embedded within the substance of tendons, are found especially at the
roots of the thumb and of the great toe, and are always placed in the
direction of flexion. Their office, like that of the patella, which is,
in truth, a bone of this class, is to increase the power of the flexor
muscles by altering the line of their direction, that is, by removing
them farther from the axis of the bone on which they are intended to
act.

199. The ligaments which connect the bones of the lower extremities
are the firmest and strongest in the body. Of these, the fibrous
capsule of the hip-joint (fig. XCIV. 1), which secures the head of the
femur in the cavity of the acetabulum (fig. XCIV.), is the thickest and
strongest. It completely surrounds the joint (fig. XCIV. 1). It arises
from the whole circumference of the acetabulum, and, proceeding in a
direction outwards and backwards, is attached below to the neck of the
femur (fig. XCIV. 1). It is thicker, stronger, and much more closely
attached to the bones than the fibrous capsule of the shoulder-joint
(144), because the hip-joint is formed, not like the shoulder-joint,
for extent of motion, but for strength. Its internal surface is
lined by synovial membrane, and its external surface is covered and
strengthened by the insertion of muscles that move the thigh-bone.
The joint is strengthened by another ligament, which passes from the
inner and fore part of the cavity of the acetabulum (fig. XCV.) to be
inserted into the head of the femur (fig. XCIV.), called the round
ligament, the office of which obviously is to hold the head of the
femur firmly in its socket.

[Illustration: Fig. XCIV.

1. The fibrous capsule of the hip-joint, laid open and turned aside to
show, 2. the round ligament in its natural position.]

[Illustration: Fig. XCV.

A view of the head of the femur drawn out of its socket, and suspended
by the round ligament, to show more clearly the action of the ligament
in retaining the head of the femur in its socket.]

200. Numerous and complicated ligaments connect the bones that form
the knee-joint (fig. XCVI.), and the strength of these powerful bands
is greatly increased by the tendons that move the leg (fig. XCVI. 5),
which pass over, and more or less surround, the joint.

[Illustration: Fig. XCVI.

General view of the ligaments of the knee-joint. 1. Lower end of the
femur; 2. upper end of the tibia; 3. upper end of the fibula; 4. the
patella; 5. united tendons of the extensor muscles; 6. ligaments of
the patella; 7. the capsular investment of the knee; 8. the internal
lateral ligament; 9. the external lateral ligaments; 10. the posterior
ligament; 11. the ligament connecting the tibia and fibula; 12. a
portion of the interosseous ligament.]

201. Strong ligaments maintain in their proper position the bones that
form the ankle-joint (fig. XCVII.), connect the bones of the tarsus
and metatarsus with one another (fig. XCVIII. 1), and articulate the
several phalanges of the toes (fig. XCVIII. 2).

[Illustration: Fig. XCVII.

General view of the posterior ligaments of the ankle-joint. 1. Lower
end of the tibia; 2. lower end of the fibula; 3. astragalus; 4. os
calcis; 5. ligament between the tibia and fibula; 6. ligament passing
from the fibula to the astragalus; 7. ligament passing from the fibula
to the os calcis; 8. ligament passing from the tibia to the astragalus.]

[Illustration: Fig. XCVIII.

General view of the ligaments of the sole of the foot. 1. Ligaments
connecting the bones of the tarsus; 2. ligaments connecting the bones
of the toes.]

202. The joint of the hip, like that of the shoulder, is capable of
flexion, extension, and rotation; but its rotatory motions are to a
much less extent, on account of the greater depth of the acetabulum and
the stronger and shorter fibrous capsule. When the femur is flexed, the
thigh is bent upon the pelvis, and its inferior extremity is carried
forwards. When it is extended, the thigh is carried backwards. The
two thighs may be separated from each other laterally (abduction), or
brought near to each other (adduction), or the one may be made to cross
the other, and they may be rotated outwards or inwards.

203. The apparatus of muscles that produces these varied motions is
seated partly on the trunk and partly on the pelvis. Thus, the powerful
muscle that flexes the thigh, or that carries it forwards, termed
the psoas (fig. XCIX. 1), arises from the last vertebra of the back,
and successively from each vertebra of the loins (fig. XCIX. 1), and
is inserted into the lesser trochanter of the femur (fig. XCIX. 3).
Its action is assisted first by a large and strong muscle named the
iliacus (fig. XCIX. 2), which occupies the whole concavity of the ilium
(fig. XCIX. 2), and which, like the psoas, is inserted into the lesser
trochanter of the femur (fig. XCIX. 3).

[Illustration: Fig. XCIX.

View of the muscles that bend the thigh. 1. The muscle called psoas;
2. the muscle called iliacus; 3. tendons of these muscles, going to be
inserted into the trochanter minor of the femur.]

204. The muscles that extend the thigh, or that carry it backwards,
named the glutæi, the most powerful muscles of the body, are placed
in successive layers, one upon the other, on the back part of the
ilium (fig. C. 1, 2, 3), and are inserted into the linea aspera of the
femur. They constitute the mass of flesh which forms the hip, and their
powerful action in drawing the thigh backwards is assisted by several
other muscles (fig. C. 4, 5, 6). Their action is never perfectly simple
and direct; for those which move the thigh forwards sometimes carry it
inwards, and sometimes outwards; and in like manner, those which move
it backwards, at one time carry it inwards and at another outwards,
according to the direction of the fibres of the muscle and the position
of the limb when those fibres act; while some of them, and more
especially those which carry it backwards, at the same time rotate it,
or roll it upon its axis.

[Illustration: Fig. C.

View of the muscles that extend the thigh. 1. The muscle called glutæus
maximus, removed from its origin, 2, 2, to show the muscles which lie
beneath it; 2. cut edge showing the origin of the same muscle; 3. the
muscle called glutæus medius; 4, 5, 6. smaller muscles, assisting the
action of the glutæi.]

205. The knee is a hinge-joint, admitting only of flexion and
extension, and is therefore provided only with two sets of muscles, one
for bending and the other for extending the leg. The flexors of the leg
arise from the under and back part of the pelvis, are seated on the
back part of the thigh, and are inserted into the upper part either of
the tibia or of the fibula (fig. CI). They consist for the most part of
three muscles, named the semi-tendinosus, the semi-membranosus (fig.
CI. 3), and the biceps of the leg (fig. CI. 1). The tendons of the two
former muscles, in passing to be inserted into the leg, form the inner,
and that of the latter the outer, hamstrings (fig. CI. 4, 5).

[Illustration: Fig. CII.

View of the flexor and extensor muscles of the leg. 1. The biceps of
the leg; 2. tendon of the biceps, inserted into the head of the fibula;
3. the semi-membranosus, passing to be inserted into the head of the
fibula; 4. tendon of the semi-membranosus forming the inner, and 5.
tendon of the biceps forming the outer, hamstring; 6. upper part of the
gastrocnemius muscle; 7. the four large muscles which unite to form the
great extensor muscle of the leg, inserted into 8. the patella; 9. a
portion of the glutæus maximus concealing the other muscles of the hip.]

206. Four large muscles, blended together in such a manner as to form
one muscle of prodigious size, termed the quadriceps cruris (fig. CI.
7), occupying nearly all the forepart and the sides, and a considerable
portion of the back part of the thigh, constitute the great flexor of
the thigh. This enormous mass of muscle arises partly from the ischium,
and partly from the upper part of the femur (fig. CI. 7), and is all
inserted into the patella (fig. CI. 8), which constitutes a pulley for
the purpose of assisting the action of these powerful muscles.

207. The muscles which bend the toes and extend the foot, termed the
gastrocnemii (fig. CII. 1, 2), are placed on the back part of the leg,
and form the mass of muscle which constitutes the calf of the leg (fig.
CII. 1, 2). They arise partly from the lower extremity of the femur
(fig. CII.) and partly from the upper and back part of the fibula and
tibia; and they form the largest and strongest tendon in the body,
termed the tendo achillis (fig. CII. 3), which is implanted into the
heel (fig. CII. 4).

[Illustration: Fig. CII.

View of the muscles which bend the toes, and which, by lifting the
heel, extend the foot. 1. The muscle called gastrocnemius externus,
which, uniting with 2. the gastrocnemius internus, forms 3. the tendo
achillis, which is inserted into 4. the heel.]

[Illustration: Fig. CIII.

View of the muscles which extend the toes and bend the foot. 1. The
common extensor; 2. the tendons of the same muscle inserted into the
toes; 3. the anterior annular ligament of the foot.]

[Illustration: Fig. CIV.

View of the muscles in the sole of the foot. 1 The muscle which draws
the great toe from the other toes; 2. the muscle which draws the little
toe from the other toes; 3. the muscle called the short flexor of the
toes, which assists in bending the four smaller toes.]

208. The muscles which extend the toes and bend the foot are seated
on the fore part of the leg (fig. CIII.); split into tendons like the
analogous muscles of the fingers (fig. CIII. 2); and are bound down
by a ligament (fig. CIII. 3), exactly the same in name, disposition,
and office, as that which belongs to the hand (fig. CIII. 3). Numerous
minute muscles are placed in the sole of the foot (fig. CIV.), which
act on the toes as the small muscles in the palm of the hand act on the
fingers (fig. LXXXVI.).

209. Such are the moving powers which put in action the complicated
mechanism provided for the function of locomotion. And these powers are
adequate to their office; but they are what may be termed expensive
powers; agents requiring a high degree, of organization and the utmost
resources of the economy to support and maintain them. Hence in the
construction of the framework of the machine which they have to move,
whatever mechanical contrivance may economize their labour, is adopted.
The construction, form, and disposition of the several parts of that
framework have all reference to two objects: first, the combination
of strength with lightness; and secondly, security to tender organs,
with the power of executing rapid, energetic, and, sometimes, violent
motions. The combination is effected and the object attained in a mode
complicated in the detail, simple in the design, and perfect in the
result. The weight of the body transmitted from the arch of the pelvis
to a second arch, formed by the neck of the thigh-bone, and from this,
in a perpendicular direction, to a third arch formed by the foot, is
ultimately received by the heel behind, and by the metatarsal bones
and the first phalanges of the toes before, and more especially by the
metatarsal joints belonging to the great and little toe, which have a
special apparatus of muscles, for the purpose of preserving steadily
their relative situation to the heel. The weight of the body is thus
sustained on a series of arches, from which it is, in succession,
transmitted to the ground, where it ultimately rests upon a tripod:
forms known and selected as the best adapted to afford support, and to
give security of position. Columns of compact bone superimposed one
upon another, and united at different points by bands of prodigious
strength, form the pillars of support. But these bony columns never
touch each other; are never in actual contact; are all separated by
layers of elastic matter which, while they assist in binding the
columns together, enable them to move one upon another, as upon so many
pliant springs. The layers of cartilage interposed between the several
vertebræ; the layer of cartilage interposed between the vertebral
column and the pelvis; the layer of cartilage that lines the acetabulum
and that covers the head of the femur; the layer of cartilage that
covers the lower extremity of the femur and the upper extremity of the
tibia and fibula and the tarsus; the successive layers of cartilage
interposed between the several bones of the tarsus; and finally,
the layer of cartilage that covers both the tarsal and the digital
extremities of the metatarsal bones; are so many special provisions to
prevent the weight of the body from being transmitted to the ground
with a shock; and, at the same time, so many barriers established
between the ground and the spinal cord, the brain and the soft and
tender organs contained in the thoracic and abdominal cavities, to
prevent these organs from being injured by the reaction of the ground
upon the body. The excellence of this mechanism is seen in its results;
in contemplating "from what heights we can leap—to what heights we can
spring—to what distances we can bound—how swiftly we can run—how
firmly we can stand—how nimbly we can dance—and yet how perfectly we
can balance ourselves upon the smallest surfaces of support!"

210. It is necessary, in order to complete this general view of the
structure of the human body, and of the combination and arrangement
of its various parts, to denote the several regions into which, for
the purpose of describing with accuracy the situation and relation of
its more important organs, the body is divided. It is not needful to
the present purpose to describe the regions of the head, because its
internal cavity contains only one organ, the brain, and its external
divisions do not differ materially from those which are common
and familiar; but the chest, the abdomen, and the upper and lower
extremities are mapped out into regions, of which it is very important
to have an exact knowledge, which may be acquired by the study of the
annexed diagrams.

[Illustration: Fig. CV.

Anterior view of the regions of the body. 1. Region of the neck; 2.
region of the chest or thorax. Abdominal regions: 3. epigastric; 4.
umbilical; 5. hypogastric region. Regions of the upper extremities. 6.
shoulder; 7. arm; 8. elbow; 9. fore-arm; 10. wrist; 11. ball of thumb;
12. the axilla or armpit. Regions of the lower extremities: 13. thigh;
14. knee; 15. leg; 16. ankle; 17. instep and foot.]

[Illustration: Fig. CVI.

Posterior view of the regions of the body: 18. region to the scapula;
19. of the back; 20. of the loins; 21. of the hips; 22. of the ham; 23.
of the calf of the leg; 24. of the heel and foot.]

[Illustration: Fig. CVII.

Lateral view of the regions of the body: 25. arch of the foot.]

[Illustration: Fig. CVIII.

Anterior view of the situation of the more important internal organs:
1. lungs, right and left; 2. heart; 3. line representing the edge of
the diaphragm; 4. liver; 5. stomach; 6. small intestines; 7. colon; 8.
urinary bladder.]

[Illustration: Fig. CIX.

Posterior view of the situation of the more important internal organs:
9. kidnies, right and left; 10. the course of the spinal cord.]

[Illustration: Fig. CX.

Lateral view of the situation of the more important internal organs.]




CHAPTER VI.

OF THE BLOOD.

  Physical characters of the blood: colour, fluidity,
  specific gravity, temperature: quantity—Process
  of coagulation—Constituents of the blood:
  proportions—Constituents of the body contained in the
  blood—Vital properties of the blood—Practical applications.


211. Supposing the human body to have been built up in the manner now
described, and to be in the full exercise of all its functions, the
integrity of its various structures is maintained, and their due action
excited by the blood. Out of this substance is formed the blandest
fluid, as the milk, and the firmest solid, as the compact bone. The
heart, capable of untiring action, as long as the blood is in contact
with its internal surface, becomes immovable soon after the supply of
this fluid is withdrawn; and in less than one minute from the time
it ceases to flow in due quantity and of proper quality through the
vessels of the brain, the eye is no longer capable of seeing, nor the
ear of hearing, nor the brain of carrying on any intellectual operation.

212. At the moment, and for some time after it has issued from its
vessel, the appearance of the blood is that of a thick, viscid, and
tenacious fluid; yet it is essentially a solid, composed of several
substances, each possessing its own distinct and peculiar properties,
the relation and combination of which cannot be considered without
exciting the feeling that our admiration of the structure of the animal
frame ought not to be confined to the mechanism of its solid parts, but
that the whole is admirable, from the common material of which it is
composed, to its most delicate and elaborate instrument.

213. The colour of redness is universally associated with the idea of
blood; but redness of colour is not essential to blood. There are many
animals with true, yet without red, blood; and there is no animal in
which the blood is red in all the parts of its body. The blood of the
insect is transparent; that of the reptile is of a yellowish colour;
that of the fish, in the greater part of its body, is colourless. Even
the red blood of the human body is not equally red in every part of it,
there being two distinct systems of blood-vessels, distinguished from
each other by carrying blood of different colours.

214. In the state of health, the specific gravity of human blood, water
being 1000, is 1080; from which standard it is capable of varying from
1120, the maximum, to 1026, the minimum.

215. The natural temperature of the human blood is 98°. From this it
is capable of varying from 104°, the maximum, to 86°, the minimum;
these changes being always the effect of disease.

216. It is estimated that the fluids circulating in the adult
man amount to about fifty pounds; of these it is calculated that
twenty-eight consist of red blood.

217. Fluid and homogeneous as the blood appears while flowing in its
vessel, when a mass of it is collected and allowed to stand at rest, it
soon undergoes a very remarkable change. First, a thin film is formed
upon its surface; this is followed by the conversion of the whole mass
into a soft jelly: this jelly separates into two portions, a fluid and
a solid portion. The solid portion again separates into two parts, into
a substance of a yellowish-white colour, occupying the upper surface,
and into a red mass always found at the under surface.

218. The process by which the constituents of the blood are thus
spontaneously disunited, and afforded in a separate form, is
denominated COAGULATION; the fluid portion separated by the process is
termed the SERUM; the solid portion the COAGULUM or CLOT; the white
substance forming the upper part of the clot, the FIBRIN; and the red
mass forming the under part of it, the RED PARTICLES.

219. Probably the process of coagulation commences the moment the
blood leaves its living vessel. In three minutes and a half it is
visible to the eye; in seven minutes the mass is formed into a jelly;
in from ten to twelve minutes the serum separates from the clot; in
about twenty the clot is divided into fibrin and red particles, when
the coagulation is complete; but occasionally the clot continues to
grow firmer and firmer for the space of twenty-four hours.

220. As soon as the coagulation commences, and during all the time the
blood preserves its heat, an aqueous vapour arises from it, termed
the HALITUS. The halitus consists of water holding in solution a
small quantity of animal and saline matter, which communicate to it a
fœtid odour of a strong and peculiar nature, manifest on approaching
a slaughter-house, and still more manifest in the slaughter-house of
human beings, a field of battle.

221. During the process of coagulation, as in every other in which a
fluid is converted into a solid, caloric is evolved.

222. During the process of coagulation carbonic acid is also extricated.

223. The process of coagulation affords three distinct substances,
the chief constituents of the blood, namely, serum, fibrin, and red
particles.

224. The serum, the fluid portion of the blood, when obtained
perfectly pure, is of a light straw colour, tinged with green.
Its taste is saline, and its consistence adhesive. It is composed
principally of water holding in solution animal and saline matter.
The animal matter gives it its adhesive consistence, and the saline
its peculiar salt taste. The chief animal matter contained in it is
the proximate principle termed albumen, which may be separated from
the water that holds it in solution by the application of heat and
by certain chemical agents. Heat being applied, when the temperature
reaches 160°, fluid serum is converted into a white opaque solid
substance of firm consistence. This is found to be albumen, which may
be also separated from the watery portion by the application of spirits
of wine, acids, oxymuriate of mercury, and several other chemical
substances. The quantity of albumen contained in 1000 parts of serum
varies from about 78, the maximum, to 58, the minimum.

225. If the albumen yielded by the serum be subjected to pressure, or
be cut into small pieces, there flows from it a watery fluid which is
termed the serosity. In meat dressed for the table, the serum of the
blood contained in the blood-vessels is converted by the heat into
solid albumen, from which, when cut, the serosity flows in the form of
gravy.

226. Besides albumen, serum holds in solution both a fatty and an oily
matter, in the proportion of about one part of each to 1000 parts of
serum. The proportion of its saline substances is about ten in 1000
parts. According to M. le Canu, who has made the most recent chemical
analysis of serum, 1000 parts contain, of

  Water                                     906·00
  Albumen                                    78·00
  Animal matter, soluble in water
    and alcohol                               1·69
  Albumen combined with soda                  2·10
  Crystallizable fatty matter                 1·20
  Oily matter                                 1·00
  Hydrochlorate of soda and
    potash                                    6·00
  Subcarbonate and phosphate of
    soda, and sulphate of potash              2·10
  Phosphate of lime, magnesia,
    and iron, with subcarbonate
    of lime and magnesia                       ·91
  Loss                                        1·00

227. All the animal and saline matter held in solution in the serum
being removed, the fluid that remains is water, the proportion of which
in 1000 parts varies from 853, the maximum, to 779, the minimum.

228. The second constituent of the blood, the fibrin, is the most
essential portion of it, being invariably present, whatever other
constituent be absent. While circulating in the living vessel,
fibrin is fluid and transparent; by the process of coagulation, it
is converted into a solid and opaque substance of a yellowish white
colour, consisting of stringy fibres, disposed in striæ, which
occasionally form a complete net-work (fig. CXI.). These fibres are
exceedingly elastic. In their general aspect and their chemical
relations they bear a close resemblance to pure muscular fibre, that
is, to muscular fibre deprived of its enveloping membrane and of its
colouring matter, and they form the basis of muscle. According to M.
le Canu, the proportion of the fibrin varies from seven parts in 1000,
the maximum, to one part in 1000, the minimum, the medium of twenty
experiments being four parts in 1000.

[Illustration: Fig. CXI.

A portion of the fibrin of the blood, showing its fibrous structure and
the striated or net-like arrangement of its fibres.]

229. The third constituent of the blood, the matter upon which its red
colour depends, though, as has been stated, entirely absent in certain
classes of animals, and in all animals in some parts of their body,
seems to be essential, at least to the organic organs, whenever they
perform their functions with a high degree of perfection. Thus in the
lowest class of vertebrated animals, the fish, while the principal part
of its body receives only a colourless fluid, its organic organs, as
the heart, the gills, the liver, are provided with red blood.

230. The red matter, wherever present, is invariably heavier than
the fibrin, and consequently, during the process of coagulation, it
gradually subsides to the lower surface, and is always found forming
the bottom of the clot. Its proportion to the other constituents varies
very remarkably, the maximum being 148, the minimum 68, and the medium
108, in 1000 parts of blood.

231. All observers are agreed that the red matter of the blood consists
of minute particles, having a peculiar and definite structure; but in
regard to the nature of that structure, there is considerable diversity
of opinion, which is not wonderful, since the particles in question
are so minute that they can be distinguished only by the microscope,
and since, of all microscopical objects, they are perhaps the most
difficult to examine, because, being soft and yielding, their figure
is apt to change, and because there is reason to suppose that their
substance is not uniform in its refractive power.

232. The earlier observers describe the red particles as being of
a globular figure, and accordingly name them globules. They conceive
that each globule consists of a central solid particle, enveloped in a
transparent vesicle. Recently, Sir Everard Home and Mr. Bauer in this
country, and MM. Prevost and Dumas on the continent, have revived this
opinion, and describe the red particle as consisting of a central solid
white corpuscle contained in an external envelop of a red colour. When
the blood is observed with the microscope in a living animal, flowing
in its vessels, only two substances can be distinguished, namely,
a transparent fluid and the red corpuscles. MM. Prevost and Dumas
contend that these two substances are the only component parts of the
blood. When the blood coagulates, they conceive that the red envelop
separates from the central white corpuscle; that these white corpuscles
unite together; that the aggregates resulting from this combination
are disposed in the form of filaments, which filaments constitute the
fibrin, while the red matter at the bottom of the clot is nothing but
the disintegrated envelops of the central particle. But this view is
not the common one. In general, physiologists conceive the fibrin to
be one constituent and the red particles to be another constituent of
the blood. Mr. Lister, who has successfully laboured to improve the
microscope, and who, together with his friend Dr. Hodgkin, have very
carefully examined with their improved instrument the red particles,
contend that the figure of these bodies is not globular, although
they state that the instant the particles are removed from the living
blood-vessels many things are capable of making them assume a globular
appearance; such, for example, as the application of water. With a
rapidity which, in spite of every precaution, the eye in vain attempts
to follow, the particles change their real figure for a globular form
on the application of the smallest quantity of pure water; while,
if the water contain a solution of saline matter, little alteration
is occasioned in the figure of the particles. According to these
observers, the red particles are flattened cakes, having rounded and
very slightly thickened margins (fig. CXII. 1). The thickness of the
margin gives to both surfaces the appearance of a slight depression
in the middle (fig. CXII. 1), so that the particles bear a close
resemblance to a penny piece. There is no appearance of an external
envelop. The circular and flattened cake is transparent; when seen
singly it is nearly if not quite colourless (fig. CXII. 1); it assumes
a reddish tinge only when aggregated in considerable masses.

[Illustration: Fig. CXII.

1. A particle of the human blood as it appears when transparent and
floating; 2. the same dry, seen as opaque, illuminated by a leiberkuhn;
3. the same as it appears when half the leiberkuhn is darkened; 4. a
particle of the frog's blood floating; 5. the same seen on its edge.
All the above objects are magnified 500 diameters[5].]

233. The red particle of the human blood is circular (fig. CXII. 1, 2,
3). It is circular also in all animals belonging to the class mammalia;
but in the three lower classes of vertebrated animals, the bird, the
reptile, and the fish, it is elliptical (fig. CXII. 4, 5).

234. The magnitude of the red particle of the human blood is variously
estimated from the two-thousandth to the six-thousandth part of an inch
in diameter. Bauer estimates it at the two-thousandth, Hodgkin and
Lister at the three-thousandth, Kater at the four-thousandth, Wollaston
at the five-thousandth, and Young at the six-thousandth part of an
inch. Its magnitude is uniformly the same in all individuals of the
same species, but differs exceedingly in the different classes. The
elliptical particles are larger than the circular, but proportionally
thinner; larger in fishes than in any other class of animals, and
largest of all in the skate.

235. When perfect and entire, the red particles indicate a disposition
to arrange themselves in a definite mode. They combine spontaneously
into columns of variable length (fig. CXIII.). In order to observe this
tendency, a small quantity of blood, the moment it is taken from its
living vessel, should be placed between two strips of glass or covered
with a bit of talc and placed under the microscope. When thus arranged,
a considerable agitation at first takes place among the particles.
As soon as this motion subsides, the particles apply themselves to
each other by their broad surfaces, and thus form piles or columns of
Considerable length (fig. CXIII.). The columns often again combine one
among another, the end of one being attached to the side of another,
sometimes producing very curious ramifications (fig. CXIII.). In
like manner, the elliptical particles apply themselves to each other
by their broad surfaces, but they are not so exactly matched as the
circular, one particle partially overlapping another, so that they form
less regular columns than the circular.

[Illustration: Fig. CXIII.

Columnar arrangement which the particles of the human blood assume
immediately after it is drawn from its vessel.]

236. The red particles, as far as is known, constitute a distinct and
peculiar form of animal matter: the red colour, according to some,
depending on an impregnation of iron; according to others, on an animal
substance of a gelatinous nature.

237. The exact proportion of the different substances contained in the
blood, according to the most recent analysis of it, that by M. le Canu,
is as follows, namely,

  Water                                786·500
  Albumen                               69·415
  Fibrin                                 3·565
  Colouring matter                     119·626
  Crystallizable fatty matter            4·300
    Oily matter                          2·270
  Extractive matter, soluble in
    alcohol and water                    1·920
  Albumen combined with soda             2·010
  Chloruret of sodium and potassium,
    alkaline phosphate,
    sulphate, and subcarbonates          7·304
  Subcarbonate of lime and magnesia,
    phosphates of lime,
    magnesia and iron, peroxide
    of iron                              1·414
  Loss                                   2·586
                                      --------
                                      1000·

238. From the results of this analysis it is manifest that all the
proximate principles of which the different tissues are composed exist
in the blood, namely, albumen, the proximate principle forming the
basis of membrane; fibrin, the proximate principle forming the basis
of muscle; fatty matter, forming the basis of nerve and brain; and
various saline and mineral substances, forming a large part of bone,
and entering more or less into the composition of every fluid and solid.

239. The blood, which contains all the proximate constituents of the
body, and which, by distributing them to the various tissues and
organs, maintains their integrity and life, is itself alive. The
vitality of the blood is proved,—

240. i. By its undergoing the process of death, which it does just as
much as the heart or the brain, every time it is removed from the body.
While flowing in its living vessel, the blood is permanently fluid.
Its fluidity depends on a force of mutual repulsion exerted by its
particles on each other. That repulsive force is a vital endowment,
probably derived from the organic nerves so abundantly distributed
to the inner coat of the blood-vessels. When this vital influence
is withdrawn, which happens on the removal of the blood from its
vessel, the mass is no longer capable of remaining fluid; the fibrin
is converted into a solid; the red particles, instead of repelling,
attract each other, forming the crude aggregate at the bottom of
the clot; coagulation is thus a process of death; its commencement
indicates a diminution of the vital energy of the blood; during its
progress that energy is constantly growing less and less; the blood is
dying; and when complete, the blood is dead.

241. Hence in every state of the system in which the vital energy of
the blood is preternaturally increased, coagulation is proportionably
slow; in every state in which its energy is diminished, coagulation
is rapid. By copious and repeated blood-letting, the vital energy
is rapidly exhausted. The effect of blood-letting on coagulation
is determined by experiments instituted for the express purpose of
ascertaining it. Blood was received from a horse at four periods, about
a minute and a half intervening between the filling of each cup.

                                      Minutes.   Seconds.

  In cup No. 1. coagulation began in     11         10
       "     2.     "     "     "        10          5
       "     3.     "     "     "         9         55
       "     4.     "     "     "         3         10

242. In like manner three cups were filled with the blood of a sheep,
at the interval of half a minute.

                                      Minutes.   Seconds.

  In cup No. 1. coagulation began in      2         10
       "     2.     "     "     "         1         45
       "     3.     "     "     "         0         55

The same result was obtained in blood taken from a human subject. A
pound and a half of blood was removed from the arm of a woman labouring
under fever, a portion of which, received into a tea-cup on the first
effusion, remained fluid for the space of seven minutes; a similar
quantity, taken immediately before tying up the arm, was coagulated
in three minutes thirty seconds. These experiments demonstrate that
coagulation is rapid or slow as the vital energy of the blood is
exhausted or unexhausted, or that in proportion to the degree of life
possessed by the blood is the space of time it takes in dying.

243. This result is referable to the principle already shown to be
characteristic of living substance,—namely, the power of resisting,
within a certain range, the ordinary influence of physical agents.
The operation of this power is illustrated in a beautiful manner in
a series of experiments performed by Mr. Hunter on the egg and on
blood. This physiologist exposed a live, that is, a fresh egg to the
temperature of the 17th and the 15th degrees of Fahrenheit; it took
half an hour to freeze it. The egg was then thawed and exposed to 10°
less cold, namely, to the 25th degree of Fahrenheit; it was now frozen
in a quarter of an hour. A living egg and one that had been killed by
having been first frozen and then thawed, were put together into a
freezing mixture at 15°: the dead was frozen twenty-five minutes sooner
than the living egg. The undiminished vitality of the fresh egg enabled
it to resist the low temperature for the space of twenty-five minutes;
the vitality of the frozen egg having been destroyed, it yielded at
once to the influence of the physical agent. On subjecting blood to
analogous experiments, the result was found to be the same. Blood
immediately taken from the living vessel, and blood previously frozen
and then thawed, being exposed to a freezing mixture, a much shorter
period and a much less degree of cold were required to freeze the
latter than the former.

244. ii. The vitality of the blood is proved by the change it
undergoes in becoming a constituent part of an organized tissue.
The blood conveys to the several tissues the constituents of which
they are composed; each tissue selects from the mass of blood its
own constituents and converts them into its own substance, in which
conversion, since the blood always goes to the tissue in a fluid
form, the blood must necessarily pass from a fluid into a solid. In
the vessels the vital endowment of the blood maintains it permanently
fluid; in the structures the same power makes it and keeps it
solid. One and the same substance in one and the same body, in one
part is always fluid, in another always solid; the fluid is every
moment passing into the solid and the solid into the fluid, without
intermixture and without interference. Nothing analogous to this is
ever witnessed in inorganic matter, in physical mechanism; it is
peculiar to the organized body and distinctive of the mechanism of
life. Sometimes in physical mechanism we can perceive the mechanical
arrangements and distinctly trace them from beginning to end: in vital
mechanism, even when we can discern the mechanical arrangements, we can
seldom trace them beyond a step or two, and never from beginning to
end; but arrangement and adaptation we know there must be in that which
goes beyond, no less than in that which keeps within, our perception,
and we ought scarcely to question the existence of adjustments, because
they elude our sense, when probably the very reason why they do so is
that their delicacy and perfection immeasurably exceed any with which
sense has made us acquainted.

245. iii. The vitality of the blood is proved by the process of
organization. We can trace only a few steps of this process, but these
are sufficient to establish the point in question. Blood effused from
living vessels into the substance, or upon the surface of living
organs, solidifies without losing vitality. If a clot of blood be
examined some time after it has thus become solid, it is found to
abound with blood-vessels. Some of these vessels are obviously derived
from the surrounding living parts. The minute vessels of these parts,
as can be distinctly traced, elongate and shoot into the clot. The
clot thus acquires blood-vessels of its own. By degrees a complete
circulation is established within it. The blood-vessels of the clot act
upon the blood they receive just as the vessels of any other part act
upon their blood, that is transform it into the animal matter it is
their office to elaborate. In this manner a clot of blood is converted
into a component part of the body, and acquires the power of exercising
its own peculiar and appropriate functions in the economy.

246. But while, in this process, some of the vessels of the clot can
be distinctly traced from the surrounding living parts, others appear
to have no communication with those parts, at all events no such
communication can be traced. These vessels, the origin of which cannot
be found external to the clot, are supposed by some physiologists to
be formed within it. Within the living egg, during incubation, certain
motions or actions are observed spontaneously to arise, which terminate
in the development of the chick. Analogous motions arising within the
clot terminate, it is conceived, in the development of blood-vessels.
According to this view, a simultaneous action takes place in the clot,
and in the living part with which it is in contact; each shooting out
vessels which elongate, approximate, unite, and thus establish a direct
vital communication. Whether this view of the process of organization
be the correct one or not does not affect the present argument. It
is certain that a clot of blood surrounded by living parts becomes
organized; it is certain that no dead substance surrounded by living
parts becomes organized; it follows that the blood possesses life.

247. Health and life depend on the quantity, quality, and distribution
of the blood. The chief source from which the blood itself is derived
is the chyle: hence too much or too little food, or too great or too
little activity of the organs that digest it, may render the quantity
of the blood preternaturally abundant or deficient; or though there be
neither excess nor deficiency in the quantity of nourishment formed,
parts of the blood which ought to be removed may be retained, or
parts which ought to be retained may be removed, and hence the actual
quantity in the system may be superabundant or insufficient.

248. The relative proportion of every constituent of the blood
is capable of varying; and of course in the degree in which the
healthy proportion is deranged, the quality of the mass must undergo
a corresponding deterioration. The watery portion is sometimes so
deficient, that the mass is obviously thickened; while at other times
the fluid preponderates so much over the solid constituents, that the
blood is thin and watery. The albumen, the quantity of which varies
considerably even in health, in disease is sometimes twice as great,
and at other times is less than half its natural proportion. In some
cases the fibrin preponderates so much, that the coagulum formed by
the blood is exceedingly coherent, firm and dense; in other cases the
quantity of fibrin is so small, that the coagulation is imperfect,
forming only a soft, loose and tender coagulum, and in extreme cases
the blood remains wholly fluid. When the vital energy of the system
is great, the red particles abound; when it is depressed, they are
deficient. In the former state, they are of a bright red colour; in
the latter, dusky, purple, or even black. When the depression of
the vital energy is extreme, the power of mutual repulsion exerted
by the particles would seem to be so far destroyed as to admit of
their adhering to each other partially in certain organs; while in
other cases they seem to be actually disorganised, and to have their
structures so broken up, that they escape from the current of the
circulation as if dissolved in the serum, through the minute vessels
intended only for the exhalation of the watery part of the blood.
This fearful change is conceived to have an intimate connexion with
a diminution of the proportion of the saline constituents. Out of
the body, as has been shown, the red particles change their figure
instantaneously, and are rapidly dissolved when in contact with
pure water; while they undergo little change of form if the water
hold saline matter in solution. It would seem that one use of the
saline constituents of the blood is to preserve entire the figure and
constitution of the red particles. It is certain that any change in the
proportion of the saline constituents produces a most powerful effect
on the condition of the red particles. It is no less certain that
changes do take place in the proportion of the saline constituents.
In the state of health, the taste of the blood is distinctly salt,
depending chiefly on the quantity of muriate of soda contained in
it. In certain violent and malignant diseases, such, for example, as
the malignant forms of fever, and more especially that form of it
termed pestilential cholera, this salt taste is scarcely, if at all,
perceptible; and it is ascertained that, in such cases, the proportion
of saline matter is sensibly diminished.

249. The quality of the blood may be also essentially changed
by the disturbance of the balance of certain organic functions:
digestion, absorption, circulation, respiration, are indispensable
to the formation of the blood and to the nourishment of the tissues.
Absorption, nutrition, secretion, circulation, render the blood impure,
either by directly communicating to it hurtful ingredients, or by
allowing noxious matters to accumulate in it, or by destroying the
relative proportion of its constituents. Organs are specially provided,
the main function of which is to separate and remove from the blood
these injurious substances. Organs of this class are called depurating,
and the process they carry on is denominated that of depuration. The
lungs, the liver, the kidneys, are depurating organs, and one result at
least of the functions they perform is the purification or depuration
of the blood. If the lung fail to eliminate carbon, the liver bile,
the kidney urine, carbon, bile, urine, or at least the constituents
of which these substances are composed, must accumulate in the blood,
contaminate it, and render it incapable of duly nourishing and
stimulating the organs.

250. But though the blood be good in quality and just in quantity,
health and life must still depend upon its proper distribution. It
may be sent out to the system too rapidly or too slowly. It may be
distributed to different portions of the system unequally; too much may
be sent to one organ, and too little to another: consequently, while
the latter languishes, the former may be oppressed, overwhelmed or
stimulated to violent and destructive action. In either case health is
disturbed and life endangered.

251. Of the mode and degree in which food, air, moisture, temperature,
repletion, abstinence, exercise, indolence, influence the quantity,
quality, and distribution of the blood; of the mode in which the
condition of the blood modifies the actions both of the organic and
the animal organs; of the reason why health and disease are wholly
dependent on those states and actions, a clear and just conception
may be formed when the several functions have been described, and the
precise office of each is understood.




CHAPTER VII.

OF THE CIRCULATION.

  Vessels connected with the heart: chambers of the
  heart—Position of the heart—Pulmonic circle:
  systemic circle—Structure of the heart, artery, and
  vein—Consequences of the discovery of the circulation to the
  discoverer—Action of the heart: sounds occasioned by its
  different movements—Contraction: dilatation—Disposition
  and action of the valves—Powers that move the blood—Force
  of the heart—Action of the arterial tubes: the pulse:
  action of the capillaries: action of the veins—Self-moving
  power of the blood—Vital endowment of the capillaries:
  functions—Practical applications.


252. The blood, being necessary to nourish the tissues and to
stimulate the organs, must be in motion in order to be borne to them.
An apparatus is provided partly for the purpose of originating an
impelling force to put the blood in motion, and partly for the purpose
of conveying the blood when in motion to the different parts of the
body.

253. The heart is the impelling organ; the great vessels in immediate
connexion with it are the transmitting organs (fig. CXIV. 1, 2). The
heart is divided into two sets of chambers (fig. CXIV. 3, 4, 10, 11),
one for the reception of the blood from the different parts of the body
(fig. CXIV. 3, 10); the other for the communication of the impulse
which keeps the blood in motion (fig. CXIV. 4, 11). The chamber which
receives the blood is termed an auricle (fig. CXIV. 3, 10), and is
connected with a vessel termed a vein (fig. CXIV. 1, 2, 9); that which
communicates impulse to the blood is termed a ventricle (fig. CXIV. 4,
11), and is connected with a vessel termed an artery (fig. CXIV. 7,
12). The vein carries blood to the auricle; the auricle transmits it to
the ventricle; the ventricle propels it into the artery; the artery,
carrying it out from the ventricle, ultimately sends it again into the
vein, the vein returns it to the auricle, the auricle to the ventricle,
the ventricle to the artery, and thus the blood is constantly moving in
a circle; hence the name of the process, the circulation of the blood.

[Illustration: Fig. CXIV.

View of the heart with its several chambers exposed, and the great
vessels in connection with them. 1. The superior vena cava; 2. the
inferior vena cava; 3. the chamber called the right auricle; 4. the
chamber called the right ventricle; 5. the line marking the passage
between the two chambers, and the points of attachment of one margin of
the valve; 6. the septum between the two ventricles; 7. the pulmonary
artery arising from the right ventricle, and dividing at 8, into right
and left for the corresponding lungs; 9. the four pulmonary veins
bringing the blood from the lungs into 10, the left auricle; 11. the
left ventricle; 12. the aorta arising from the left ventricle, and
passing down behind the heart to distribute blood, by its divisions and
subdivisions, to every part of the body.]

254. In nourishing the tissues and stimulating the organs, the blood
parts with its nutritive and stimulating constituents, and receives in
return some ingredients which can no longer be usefully employed in the
economy, and others which are positively injurious. An apparatus is
established for its renovation and depuration; this organ is termed the
lung (fig. LIX. 5), and to this organ the blood must in like manner be
conveyed. Thus the blood moves in a double circle, one from the heart
to the body and from the body back to the heart, termed the systemic
circle; the other from the heart to the lung and from the lung back
to the heart, termed the pulmonic circle. Hence in the human body the
heart is double, consisting of two corresponding parts precisely the
same in name, in nature, and in office; the one appropriated to the
greater, or the systemic, and the other to the lesser, or the pulmonic
circulation (fig. CXIV.).

255. There is a complete separation between these two portions of the
heart (fig. CXIV. 6), formed by a strong muscular partition which
prevents any communication between them except through the medium of
vessels.

256. The heart is situated between the two lungs (fig. LIX. 2, 5),
in the lower and fore part of the chest, nearly in the centre, but
inclining a little to the left side. Its position is oblique (fig.
LIX. 2, 5). Its basis is directed upwards, backwards, and towards the
right (fig. LIX. 2); its apex is directed downwards, forwards, and
towards the left, opposite to the interval between the cartilages
of the fifth and sixth ribs (fig. LIX. 2). It is inclosed in a bag
termed the pericardium (fig. CXV.), which consists of serous membrane.
The pericardium is considerably larger than the heart, allowing
abundant space for the action of the organ (fig. CXV.). One part of
the pericardium forms a bag around the heart (fig. CXV.); the other
part is reflected upon the heart so as to form its external covering
(fig. CXV.), and is continued for a considerable distance upon the
great vessels that go to and from the heart in such a manner that this
bag, like all the serous membranes, constitutes a shut sac. Both that
portion of the pericardium which is reflected upon the heart, and that
which forms the internal surface of the bag around it, is moistened
during life by a serous fluid, which, after death, is condensed into a
small quantity of transparent water. That portion of the pericardium
which rests on the diaphragm (fig. LXX. 1) is so firmly attached to it
that it cannot be separated without laceration, and by this attachment,
together with the great vessels at its base, the heart is firmly held
in its situation, although in the varied movements of the body it is
capable of deviating to a slight extent from the exact position here
described.

[Illustration: Fig. CXV.

View of the heart enveloped in its pericardium, the fore part of the
latter being cut open and reflected back.]

257. When the interior of the heart is laid open there are brought
into view four chambers (fig. CXIV. 3, 4, 10, 11), two for each circle.
Those belonging to the pulmonic circle are on the right (fig. CXIV. 3,
4), those to the systemic on the left side of the body (fig. CXIV. 10,
11); hence the terms right and left are applied to these respective
parts of the heart.

258. The veins which carry the blood to the right or the pulmonic
chambers are two, one of which brings it from the upper, and the other
from the lower parts of the body: the first is called the superior and
the second the inferior vena cava (fig. CXIV. 1, 2). Both pour their
blood into the first chamber, termed the right auricle (fig. CXIV.
3); from the right auricle the blood passes into the second chamber,
denominated the right ventricle (fig. CXIV. 4): from which springs
the artery which carries the blood from the heart to the lung, the
pulmonary artery (fig. CXIV. 7). This is the pulmonic circle. From
the lung the blood is returned to the heart by four veins, termed the
pulmonary veins (fig. CXIV. 9), which pour the blood into the third
chamber of the heart, the left auricle (fig. CXIV. 10). From the left
auricle it passes into the fourth chamber, the left ventricle (fig.
CXIV. 11), from which springs the artery which carries out the blood
to the system, termed the aorta (figs. CXIV. 12, and CXVII. 11). This
is the systemic circle. In the system the minute branches of the aorta
unite with the minute branches that form the venæ cavæ, which return
the blood to the right auricle of the heart, and thus the double circle
is completed.

259. The two chambers called the auricles occupy the basis of the
heart (fig. CXIV. 3, 10). The right auricle is situated at the basis
of the right ventricle (figs. CXIV. 3, and CXVI. 4). It is partly
membranous and partly muscular. At its upper and back part is the
opening of the vena cava superior (fig. CXVI. 1), which returns the
blood to the heart from the head, neck, and all the upper parts of the
body. At its lower part is the opening of the vena cava inferior (fig.
CXVI. 2), which returns the blood from all the lower parts of the body.

[Illustration: Fig. CXVI.

View of the heart with the great vessels in connection with it, on the
right side, its different chambers being laid open and its structure
shown. 1. The vena cava superior; 2. the vena cava inferior; 3. cut
edge of the right auricle turned aside to show, 4. the cavity of the
right auricle into which the two venæ cavæ pour the blood returned
from all parts of the body; 5. hook suspending the reflected portion
of the wall of the auricle; 6. the right ventricle; 7. cut edge of the
wall of the ventricle, a portion of which has been removed to show 8.
the cavity of the ventricle; 9. situation of the opening between the
auricle and ventricle, called the auricular orifice of the ventricle;
10. valve placed between the auricle and ventricle, one margin being
firmly attached to the auriculo-ventricular opening in its entire
extent, the other lying loose in the cavity of the ventricle; 11.
probe passed from the auricle into the ventricle underneath the valve,
showing the course of the blood from the former chamber to the latter;
12. the columnæ carneæ attached by one extremity to the walls of the
ventricle, the other extremity ending in tendinous threads attached to
the loose margin of the valve; 13. passage to the pulmonary artery;
14. the three semilunar valves placed at the commencement of 15. the
pulmonary artery; 16. the two great branches into which the trunk of
the pulmonary artery divides, one branch going to each lung.]

260. The auricle communicates with its corresponding ventricle by a
large opening, termed the auricular orifice of the ventricle (figs.
CXIV. 5, and CXVI. 9). All around the opening is placed a thin but
strong membrane (fig. CXVI. 10), one margin of which is firmly attached
to the wall of the ventricle (figs. CXIV. 5, and CXVI. 9), while the
other is free (fig. CXVI. 10). This membrane receives the name, and, as
will be seen immediately, performs the office of a valve.

261. The ventricle is much thicker and proportionally stronger than the
auricle (fig. CXVI. 3, 6). It is composed almost entirely of muscular
fibre. Over nearly the whole extent of its internal surface are placed
irregular masses of muscular fibres, many of which stand out from the
wall of the ventricle like columns or pillars (fig. CXVI. 12); hence
they are called fleshy columns (columnæ carneæ). Some of these fleshy
columns are adherent by one extremity to the wall of the ventricle,
while the other extremity terminates in tendinous threads which are
attached to the membrane that forms the valve (fig. CXVI. 12).

262. From the upper and right side of this chamber springs the
pulmonary artery (fig. CXVI. 15); at the entrance of which are placed
three membranes of a crescent or semilunar shape, termed the semilunar
valves (fig. CXVI. 14).

263. The structure of the left side of the heart is perfectly analogous
to that of the right. Its auricle, like that on the left side, is
placed at the base of the ventricle (figs. CXIV. 10, and CXVII. 2), and
like it also is thin, being composed chiefly of membrane. At its upper
and back part (figs. CXIV. 9, and CXVII. 1) are the openings of the
four pulmonary veins, two from the right, and two from the left lung.

264. At the passage of communication between the left auricle and
ventricle is placed a valve analogous to that on the right side (fig.
CXVII. 7).

[Illustration: Fig. CXVII.

View of the heart with the great vessels in connection with it, on the
left side, its chambers being laid open as in the preceding figure.
1. The four pulmonary veins opening into, 2. the cavity of the left
auricle; 3. the cut edge of the wall of the auricle; 4. the appendix
of the auricle; 5. the cavity of the left ventricle; 6. the cut edge
of the wall of the ventricle, the greater portion of the wall having
been removed to show the interior of the chamber; 7. valve placed
between the auricle and ventricle; 8. columnæ carneæ terminating in
tendinous threads attached to the loose margin of the valve; 9. probe
passed underneath the valve and its tendinous threads, raising them
from the wall of the ventricle similar to a refluent current of blood;
10. passage to 11. the aorta; 12. two of the semilunar valves placed
at the mouth of the aorta, the third having been cut away; 13. arch of
the aorta; 14. the three semilunar valves at the commencement of the
pulmonary artery seen in action, completely closing the mouth of the
vessel.]

265. The walls of the left ventricle are nearly as thick again as those
of the right, and its fleshy columns are much larger and stronger. From
the upper and back part of this fourth chamber (fig. CXVII. 11) springs
the great systemic artery, the aorta, around the mouth of which are
placed three semilunar valves (fig. CXVII. 12), similar to those at the
mouth of the pulmonary artery.

266. The partition which divides the two sets of chambers from each
other (fig. CXIV. 6) is wholly composed of muscular fibres, and is
called the septum of the heart.

267. The external surface of the heart is covered by a thin but
strong membrane continued over it from the pericardium. Between this
membranous covering and its fleshy substance is lodged, even when the
body is reduced to the greatest degree of thinness, a quantity of
fat. Immediately beneath this fat are the fleshy fibres that compose
the main bulk of the organ. These fibres are arranged in a peculiar
manner. The arrangement is not perceptible when the heart is examined
in its natural state, but after it has been subjected to long-continued
boiling, which, besides separating extraneous matters from the fibres,
hardens and loosens without displacing them, the manner in which they
are disposed is manifest. Just at the point where the muscular fibres
that constitute the septum of the auricles are set upon those which
form the septum of the ventricles, and parallel with the origin of the
aorta, the heart is not muscular but tendinous. The substance called
tendon, it has been shown, is often employed in the body to afford
origin or insertion to muscular fibres, performing, in fact, the
ordinary office of bone, and substituted for it in situations where
bone would be inconvenient. From the tendinous matter just indicated
most of the fibres that constitute the muscular walls of the heart
take their origin. From this point the fibres proceed in different
directions: those which go to form the wall of the auricles ascend;
those which form the wall of the ventricles pursue an oblique course
downwards, and the arrangement of the whole is such, that a general
contraction of the fibres must necessarily bring all the parts of the
heart towards this central tendinous point. The object and the result
of this arrangement will be manifest immediately.

268. The internal surface of the chambers of the heart, in its whole
extent, is lined by a fine transparent serous membrane, which renders
it smooth and moist; and, like all other organs which have important
functions to perform, it is plentifully supplied with blood-vessels and
nerves.

269. Such is the structure of the organ that moves the blood. The
artery, the tube that carries it out from the heart, is a vessel
composed of three distinct layers of membrane superimposed one upon
another, and intimately united by delicate cellular tissue. These
layers are termed tunics or coats. The external coat (fig. CXVIII. 3),
which is also called the cellular, consists of minute whitish fibres,
which are dense and tough, and closely interlaced together in every
direction. They form a membrane of great strength, the elasticity of
which, especially in the longitudinal direction, is such that, in
addition to its other names, it has received that of the elastic coat.

[Illustration: Fig. CXVIII.

Portion of an artery, showing the several coats of which it is composed
separated from each other. 1. The internal or serous coat; 2. the
middle or fibrous coat; 3. the external or cellular coat.]

270. The middle or the fibrous tunic is composed of yellowish
flattened fibres which pass in an oblique direction around the calibre
of the vessel, forming segments of circles, which, uniting, produce
complete rings (fig. CXVIII. 2). This tunic is thick, consisting of
several layers of fibres which it is easy to peel off in succession.
They form a firm, solid, elastic, but, at the same time, brittle
membrane.

271. The inner tunic, thin, colourless, nearly transparent, and
perfectly smooth, is moistened by a serous fluid, and is thence called
the serous coat (fig. CXVIII. 1). To the naked eye it presents no
appearance of fibres, yet notwithstanding its extreme delicacy, it is
so strong that, after the other coats of the artery have been entirely
removed in a living animal, it is capable of resisting the impetus of
the circulation, and of preventing the dilatation of the artery. The
arteries themselves are supplied with arteries, vessels that nourish
their tissues, and which are sent to them from neighbouring branches,
seldom or never from the vessel itself to which they are distributed.
Each individual part of an artery is supplied by its own appropriate
vessels, which form but few communications above and below, so that
if care be not taken in surgical operations to disturb these nutrient
arteries very little, the vessel will perish for want of sustenance.

272. The vein, the tube that carries back the blood to the heart,
is composed of the same number of tunics as the artery, which, with
the exception of the middle, are essentially the same in structure,
but they are all much thinner. The external tunic consists of a less
dense and strong cellular membrane; the middle tunic, instead of being
formed of elastic rings, is composed of soft and yielding fibres,
disposed in a longitudinal direction; while the inner coat, which is
still more delicate than that of the artery, is arranged in a peculiar
manner. The inner coat of most veins, at slight intervals, is formed
into folds (fig. CXX. 5), one margin of which is firmly adherent to
the circumference of the vessel, while the other margin is free and
turned in the direction of the heart. These membranous folds are termed
valves. In all veins the diameter of which is less than a line the
valves are single; in most veins of greater magnitude they are placed
in pairs, while in some of the larger trunks they are triple, and in
a few instances quadruple, and even quintuple. The veins, like the
arteries, are supplied with nutrient vessels and nerves.

273. All the arteries of the body proceed from the two trunks already
described; that connected with the pulmonic circle, the pulmonary
artery, and that connected with the systemic circle, the aorta. These
vessels, as they go out from the heart and proceed to their ultimate
termination, are arborescent, that is, they successively increase in
number and diminish in size, like the branches of a tree going off from
the trunk (fig. CXIX. 1, 2, 3). Each trunk usually ends by dividing
into two or more branches (fig. CXIX. 1, 2), the combined area of which
is always greater than that of the trunk from which they spring, in
the proportion of about one and a half to one. As the branch proceeds
to its ultimate termination it divides and subdivides, until at length
the vessel becomes so minute, that it can no longer be distinguished
by the eye. These ultimate branches are called capillary vessels,
from their hair-like smallness (fig. CXIX. 4); but this term does not
adequately express their minuteness. It has been stated (234) that the
red particle of the blood, at the medium calculation, is not more than
the three-thousandth part of an inch in diameter; yet vast numbers of
the capillary vessels are so small that they are incapable of admitting
one of these particles, and receive only the colourless portion of the
blood.

[Illustration: Fig. CXIX.

View of the manner in which an artery divides and subdivides into its
ultimate branches. 1. Trunk of the artery; 2. large branches into which
it subdivides; 3. small branches, successively becoming smaller and
smaller until they terminate in 4. the capillary branches.]

274. Every portion of an artery, by reason of the elasticity of its
coats, preserves nearly a cylindrical form, and as the area of the
branches is greater than that of the trunks, the blood, in proceeding
from the heart to the capillaries, though passing through a series of
descending cylinders, is really flowing through an enlarging space.

275. The disposition of the veins, like that of the arteries, is
arborescent, but in an inverse order; for the course of the veins is
from capillary vessels to visible branches, and from visible branches
to large trunks (fig. CXX. 1, 2, 3). In every part of the body where
the capillary arteries terminate the capillary veins begin, and
the branches uniting to form trunks, and the small to form large
trunks, and the trunks always advancing towards the heart, and always
increasing in magnitude as they approach it, form at length the two
veins which it has been stated (258) return all the blood of the body
to the right auricle of the heart.

[Illustration: Fig. CXX.

View of the manner in which the minute branches of the vein unite to
form the larger branches and the trunks. 1. Capillary venous branches;
2. small branches formed by the union of the capillary; 3. larger
branches formed by the union of the smaller and gradually increasing in
size, to form the great trunk, 4. a portion of which is laid open to
show its inner surface and the arrangement of 5. the valves formed by
its inner coat.]

276. The veins are very much more numerous than the arteries, for
they often consist of double sets, and they are at the same time
more capacious and more extensible. Reckoning the whole of the blood
at one-fifth of the weight of the body, it is estimated that, of
this quantity, about one-fourth is in the arterial and the remaining
three-fourths in the venous system. The combined area of the branches
of the veins is much greater than that of the two trunks in which they
terminate (fig. CXX. 1, 2, 3, 4): the blood, therefore, in returning to
the heart, is always flowing from a large into a smaller space.

277. The divisions and subdivisions of the artery freely communicate
in all parts of the body by means of what are called anastomosing
branches, and this communication of branch with branch and trunk with
trunk is termed anastomosis. The same intercommunication, but with
still greater freedom and frequency, takes place among the branches
of veins. In both orders of vessels the communication is frequent in
proportion to the minuteness of the branch and its distance from the
heart. It is also more frequent in proportion as a part is exposed
to pressure; hence the minute arteries and veins about a joint are
distinguished for the multitude of their anastomosing branches; and
above all, it is frequent in proportion to the importance of the organ;
hence the most remarkable anastomosis in the body is in the brain. By
this provision care is taken that no part be deprived of its supply of
blood; for if one channel be blocked up, a hundred more are open to the
current, and the transmission of it to any particular region or organ
by two or more channels, instead of through one trunk, is a part of the
same provision. Thus the fore-arm possesses four principal arteries
with corresponding veins, and the brain receives its blood through four
totally independent canals[6].

278. That the blood is really a flowing stream, and that it pursues the
course described (258), is indubitable. For,

(1.) With the microscope, in the transparent parts of animals, the
blood can be seen in motion (fig. CXXI.); and if its course be
attentively observed, its route may be clearly traced.

[Illustration: Fig. CXXI.

View of the circulation of the blood as seen under the microscope in
the web of the frog's foot.]

(2.) The membranes termed valves are so placed as to allow of the
freest passage to the blood in the circle described, while they either
altogether prevent or exceedingly impede its movement in any other
direction.

(3.) The effect of a ligature placed around a vein and an artery, and
of a puncture made above the ligature in the one vessel and below it in
the other, demonstrate both the motion of the blood and the course of
it. When a ligature is placed around a vein, that part of the vessel
which is most distant from the heart becomes full and turgid on account
of the accumulation of blood in it; while the part of the vessel which
is between the ligature and the heart becomes empty and flaccid,
because it has carried on its contents to the heart, and it can receive
no fresh supply from the body. When, on the contrary, a ligature is
placed around an artery, that portion of the vessel which lies between
the ligature and the heart becomes full and turgid, and the other
portion empty and flaccid. This can only be because the contents of
the two vessels move in opposite directions,—from the heart to the
artery, from the artery to the vein, and from the vein to the heart.
At the same time, if the vein be punctured above the ligature, there
will be little or no loss of blood; while if it be punctured below
the ligature, the blood will continue to flow until the loss of it
occasions death, which could not be unless the blood were in motion,
nor unless the direction of its course were from the artery to the vein
and from the vein to the heart.

(4.) If fluids be injected into the veins or arteries, whether of the
dead or of the living body, they readily make their way and fill the
vessels, if thrown in the direction stated to be the natural course
of the circulation; but they are strongly resisted if forced in the
opposite direction.

279. Such is the description, and with the exception of the first
proof, such the evidence of the circulation of the blood in the
human body, pretty much as it was given by the discoverer of it, the
illustrious Harvey. Before the time of Harvey, a vague and indistinct
conception that the blood was not without motion in the body had been
formed by several anatomists. It is analogous to the ordinary mode
in which the human mind arrives at discovery (chap. iii., p. 103),
that many minds should have an imperfect perception of an unknown
truth, before some one mind sees it in its completeness and fully
discloses it. Having, about the year 1620, succeeded in completely
tracing the circle in which the blood moves, and having at that
time collected all the evidence of the fact, with a rare degree of
philosophical forbearance, Harvey still spent no less than eight years
in re-examining the subject, and in maturing the proof of every point,
before he ventured to speak of it in public. The brief tract which at
length he published was written with extreme simplicity, clearness,
and perspicuity, and has been justly characterised as one of the most
admirable examples of a series of arguments deduced from observation
and experiment that ever appeared on any subject.

280. Cotemporaries are seldom grateful to discoverers. More than one
instance is on record in which a man has injured his fortune and lost
his happiness through the elucidation and establishment of a truth
which has given him immortality. It may be that there are physical
truths yet to be brought to light, to say nothing of new applications
of old truths, which, if they could be announced and demonstrated
to-day, would be the ruin of the discoverer. It is certain that there
are moral truths to be discovered, expounded, and enforced, which, if
any man had now penetration enough to see them, and courage enough to
express them, would cause him to be regarded by the present generation
with horror and detestation. Perhaps, during those eight years of
re-examination, the discoverer of the circulation sometimes endeavoured
in imagination to trace the effect which the stupendous fact at the
knowledge of which he had arrived would have on the progress of his
favourite science; and, it may be, the hope and the expectation
occasionally arose that the inestimable benefit he was about to confer
on his fellow men would secure to him some portion of their esteem
and confidence. What must have been his disappointment when he found,
after the publication of his tract, that the little practice he had
had as a physician, by degrees fell off. He was too speculative,
too theoretical, not practical. Such was the view taken even by his
friends. His enemies saw in his tract nothing but indications of a
presumptuous mind that dared to call in question the revered authority
of the ancients; and some of them saw, moreover, indications of a
malignant mind, that conceived and defended doctrines which, if not
checked, would undermine the very foundations of morality and religion.
When the evidence of the truth became irresistible, then these persons
suddenly turned round and said, that it was all known before, and
that the sole merit of this vaunted discoverer consisted in having
circulated the circulation. The pun was not fatal to the future fame of
this truly great man, nor even to the gradual though slow return of the
public confidence even during his own time; for he lived to attain the
summit of reputation.

281. It is then indubitably established that the whole blood of the
body in successive streams is collected and concentrated at the heart.
The object of the accumulation of a certain mass of it at this organ
is to subject it to the action of a strong muscle, and thereby to
determine its transmission with adequate force and precision through
the different sets of capillary vessels.

282. In the accomplishment of this object the heart performs a twofold
action; that of contraction and that of dilatation. The auricles
contract and thereby diminish their cavities, then dilate and thereby
expand them, and the one action alternates with the other. There is the
like alternate contraction and dilatation of the ventricles. The first
action is termed systole, the second diastole, and both are performed
with force.

283. When the heart is laid open to view in a living animal, and its
movements are carefully observed, it is apparent that the two auricles
contract together; that the two ventricles contract together; that
these motions alternate with each other, and that they proceed in
regular succession. The interval between these alternate movements is,
however, exceedingly short, and can scarcely be perceived when the
heart is acting with full vigour; but it is evident when its action is
somewhat languid.

284. When the ventricles contract, the apex of the heart is drawn
upwards, and at the same time raised or tilted forwards. It is during
this systole of the ventricles, and in consequence of this result of
their action, that the apex of the heart gives that impulse against the
walls of the chest which is felt in the natural state between the fifth
and sixth ribs, and which just perceptibly precedes the pulse at the
wrist.

285. When the ear is applied to the human chest, over the situation of
the heart, a dull and somewhat prolonged sound is heard, which precedes
and accompanies the impulse of the heart against the chest. This dull
sound is immediately succeeded by a shorter and sharper sound: after
this there is a short pause; and then the dull sound and impulse are
again renewed. The duller sound and stronger impulse are ascribed to
the contraction of the ventricles, and the sharper sound and feebler
impulse to that of the auricles.

286. The movement of the heart is effected by the contraction of its
muscular fibres. Those fibres rest, as upon a firm support, on the
tendinous matter to which they are attached, from which they diverge,
and towards which their contraction must necessarily bring all the
parts of the heart (267). The result of their contraction is the
powerful compression of all the chambers of the heart, and thereby the
forcible ejection of their contents through the natural openings.

287. But the chambers, alternately with forcible contraction, perform
the action of forcible dilatation. This movement of dilatation is
effected by the reaction of the elasticity of the tendinous matter on
which the muscular fibres are supported (267). This highly elastic
substance, by the contraction of the fibres, is brought into a state of
extreme tension. The contraction of the fibres ceasing, that moment the
tense tendon recoils with a force exactly proportionate to the degree
of tension into which it had been brought. Thus the very agent that is
employed forcibly to close the chamber is made the main instrument of
securing its instantaneous re-opening. A vital energy is appointed to
accomplish what is indispensable, and what nothing else can effect,
the origination of a motive power; a physical agent is conjoined to
perform the easier task to which it is competent; and the two powers,
the vital and the physical, work in harmony, each acting alternately,
and each, with undeviating regularity and unfailing energy, fulfilling
its appropriate office.

288. When the chambers of the heart which open into each other, and
which as freely communicate with the great vessels that enter and
proceed from them, are forcibly closed, and the blood they contain is
projected from them, how is one uniform forward direction given to the
current? Why, when the right ventricle contracts, is the blood not sent
back into the right auricle, as well as forward into the pulmonary
artery? There is but one mode of preventing such an event, which is to
place a flood-gate between the two chambers; and there a flood-gate
is placed, and that flood-gate is the valve. As long as the blood
proceeds onwards in the direct course of the circulation, it presses
this membrane close to the side of the heart, and thereby prevents it
from occasioning any impediment to the current. When, on the contrary,
the blood is forced backwards, and attempts to re-enter the auricle,
being of course driven in all directions, some of it passes between the
wall of the ventricle and the valve. The moment it is in this situation
it raises up the valve, carries it over the mouth of the passage, and
shuts up the channel. There cannot be a more perfect flood-gate.

289. This is beautiful mechanism; but there is another arrangement
which surpasses mere mechanism, however beautiful. It has been shown
(260) that one edge of the membrane that forms the valve is firmly
adherent to the wall of the ventricle, while the other edge, when not
in action, appears to lie loosely in the ventricle (fig. CXVI. 10).
Were this edge really loose the refluent current would carry it back
completely into the auricle, and so counteract its action as a valve;
but it is attached to the tendinous threads proceeding from the fleshy
columns that stand along the wall of the ventricle (fig. CXVI. 12). By
these tendinous threads, as by so many strings, the membrane is firmly
held in its proper position (fig. CXVI. 10, 12); and the refluent
current cannot carry it into the auricle. Thus far the arrangement is
mechanical. But each of these fleshy columns is a muscle, exerting
a proper muscular action. Among the stimulants which excite the
contractility of the muscular fibre, one of the most powerful is
distension. The refluent current distends the membrane; the distension
of the membrane stretches the tendinous threads attached to it; the
stretching of its tendinous threads stretches the fleshy column; by
this distension of the column it is excited to contraction; by the
contraction of the column its thread is shortened; by the shortening
of the thread the valve is tightened, and that in the exact degree
in which the thread is shortened. So, the greater the impetus of the
refluent blood, the greater the distension of the membrane; and the
greater the distension of the membrane, the greater the excitement of
the fleshy column; the greater the energy with which it is stimulated
to act, the greater, therefore, the security that the valve will be
held just in the position that is required, with exactly the force that
is needed. Here, then, is a flood-gate not only well constructed as far
as regards the mechanical arrangement, but so endowed as to be able to
act with additional force whenever additional force is requisite; to
put forth on every occasion, as the occasion arises, just the degree of
strength required, and no more.

290. The contraction of the heart is the power that moves the blood;
and this contraction generates a force which is adequate to impel it
through the circle. From experiments performed by Dr. Hales it appears
that if the artery of a large animal, such as the horse, be made to
communicate with an upright tube, the blood will ascend in the tube to
the height of about ten feet above the level of the heart, and will
afterwards continue there rising and falling a few inches with each
pulsation of the heart. In this animal, then, the heart acts with a
force capable of maintaining a column of ten feet. Now a column of ten
feet indicates a pressure of about four pounds and a half in a square
inch of surface. Suppose the human heart to be capable of supporting
a column of blood eight feet high, this will indicate a pressure of
four pounds to the square inch; but the left ventricle of the heart,
while it injects its column of blood into the aorta, has to overcome
the inertia of the quantity of blood projected; of the mass already
in the artery, and of the elasticity of the vessel yielding to a
momentary increase of pressure: it is probable, therefore, that the
heart acts with a force of six pounds on the inch. The left ventricle,
when distended, has about ten square inches of internal surface;
consequently the whole force exerted by it may be about sixty pounds.
According to the calculation of Hales, it is fifty-one and a half.
Now, it is proved by numerous experiments, that, after death, a slight
impulse with the syringe, certainly much less than that which is acting
upon the blood in the same artery during life, is sufficient to propel
a solution of indigo, or fresh drawn blood, from a large artery into
the extreme capillary. If, therefore, after death, a slight force will
fill the capillaries, a force during life equal to sixty pounds must be
adequate to do so.

291. The heart, with a force equal to the pressure of sixty pounds,
propels into the artery two ounces of blood at every contraction. It
contracts four thousand times in an hour. There passes through the
heart, therefore, every hour, eight thousand ounces or seven hundred
pounds of blood. It has been stated (216) that the whole mass of blood
in an adult is about twenty-eight pounds: on an average the entire
circulation is completed in two minutes and a half; consequently a
quantity of blood equal to the whole mass passes through the heart
from twenty to twenty-four times in an hour. But though the average
space of time requisite to accomplish a complete circulation may be
two minutes and a half, yet when a stream of blood leaves the heart,
different portions of it must finish their circle at very different
periods, depending in part upon the length of the course which they
have to go, and in part upon the degree of resistance that obstructs
their passage. A part of the stream, it is obvious, finishes its course
in circulating through the heart itself; another portion takes a longer
circuit through the chest; another extends the circle round the head;
and another visits the part placed at the remotest distance from the
central moving power. Such is the velocity with which the current
sometimes goes, that, in the horse, a fluid injected into the great
vein of the neck, on one side, has been detected in the vein on the
opposite side, and even in the vein of the foot, within half a minute.

292. It has been shown (282) that the different chambers of the
heart have a tendency to perform their movements in a uniform manner,
and in a successive order; that they contract and dilate in regular
alternation, and at equal intervals; but, moreover, they continue
these movements equally without rest and without fatigue. On go the
motions, night and day, for eighty years together, at the rate of
a hundred thousand strokes every twenty-four hours, alike without
disorder, cessation, or weariness. The muscles of the arm tire after
an hour's exertion, are exhausted after a day's labour, and can by no
effort be made to work beyond a certain period. There is no appreciable
difference between the muscular substance of the heart and that of the
arm. It is true that the heart is placed under one condition which
is peculiar. Muscles contract on the application of stimuli; and
different muscles are obedient to different stimuli,—the voluntary
muscles to the stimulus of volition, and the heart to that of the
blood. The exertion of volition is not constant, but occasional; the
muscle acts only when it is excited by the application of its stimulus:
hence the voluntary muscle has considerable intervals of rest. The
blood, on the contrary, is conveyed to the heart without ceasing, in a
determinate manner, in a successive order; and this is the reason why
through life its action is uniform: it uniformly receives a due supply
of its appropriate stimulus. But why it is unwearied, why it never
requires rest, we do not know. We know the necessities of the system
which render it indispensable that it should be capable of untiring
action, for we know that the first hour of its repose would be the
last of life; but of the mode in which this wonderful endowment is
communicated, or of the relations upon which it is dependent, we are
wholly ignorant.

293. The force exerted by the heart is vital. It is distinguished from
mechanical force in being produced by the very engine that exerts it.
In the best-constructed machinery there is no real generation of power.
There is merely concentration and direction of it. In the recoil of the
spring, in the reaction of condensed steam, the energy of the expansive
impulse is never greater than the force employed to compress or
condense, and the moment this power is expended all capacity of motion
is at an end. But the heart produces a force equal to the pressure of
sixty pounds by the gentlest application of a bland fluid. Here no
force is communicated to be again given out, as in every mechanical
moving power; but it is new power, power really and properly generated;
and this power is the result of vital action, and is never in any case
the result of action that is not vital.

294. The heart projects the blood with a given force into the arterial
tubes. The arteries in the living body are always filled to distension,
and somewhat beyond it, by the quantity of blood that is in them. It
has been shown that the elasticity of their coats is such as to give
to them, even after death, the form of open hollow cylinders (274).
During life they are kept in a state of distension by the quantity of
blood they contain. By virtue of their elasticity they react upon
their contents with a force exactly proportioned to the degree of their
distension, that is, with a force at least adequate to keep them always
open and rigid.

295. These open and rigid tubes, already filled to distension, and
somewhat beyond it, receive at every contraction of the heart a
forcible injection of a new wave of blood. The first effect of the
injection of this new wave into a tube previously full to distension,
is to cause the current to proceed by jerks or jets, each jerk or
jet corresponding to the contraction of the heart. And, accordingly,
by this jet-like motion, the flow of the blood in the artery is
distinguished from that in the vein, in which latter vessel the current
is an equal and tranquil stream.

296. The second effect of this new wave is to occasion some further
distension of the already distended artery, and accordingly, when
the vessel is exposed in a living animal, and its action carefully
observed, a slight augmentation of its diameter is distinguishable at
every contraction of the heart. This new wave while it distends must at
the same time slightly elongate the vessel; cause its straight portions
to bend a little, and its curved portions to bend still more; and,
consequently, in some situations, to lift it a little from its place,
giving it a slight degree of locomotion;—and these two causes combined
produce the pulse. When the finger is pressed gently on an artery, at
the instant of the contraction of the heart, the vessel is felt to
bound against the finger with a certain degree of force: this, as just
stated, is owing to a slight distension of the vessel by the new wave
of blood, together with a slight elongation of it, and a gentle rising
from its situation.

297. The blood, in flowing through the arterial trunks and branches
to the capillaries, through the arterial to the venous capillaries, and
through the venous branches and trunks back to the heart, is exposed
to numerous and powerful causes of retardation: such, for example,
as the friction between the blood and the sides of the vessels, the
numerous curves and angles formed by the branches in springing from the
trunks, the tortuous course of the vessels in many parts of the body,
and the increasing area of the arterial branches as they multiply and
subdivide. Yet the extraordinary fact has been recently discovered,
that the blood moves with the same momentum or force in every part of
the arterial system, in the aorta, in the artery in the neck which
carries the blood to the head (the carotid artery), in the artery of
the arm (the humeral artery), in the artery of the lower extremity
(the femoral artery); in a word, in the minute and remote capillary,
and in the large trunk near the heart. Having contrived an instrument
by which the force of the blood as it flows in its vessel could be
accurately indicated by the rise of mercury in a tube, M. Poiseuille
found that the elevation of the mercury is uniformly the same in the
different arteries of the same animal, whatever the size of the artery
and its distance from the heart. This tube was inserted, for example,
into the common carotid artery of a horse: the diameter of the vessel
was 34/100ths of an inch; its distance from the heart was thirty-nine
inches; the height to which the mercury rose in the graduated tube was
accurately marked. The tube was then inserted into a muscular branch of
the artery in the thigh: the diameter of this vessel was 7/100ths of an
inch, and its distance from the heart 67½ inches. According to the mean
of nine observations, the mercury rose in both tubes to precisely the
same elevation. Here is another instance of the beautiful adjustments
everywhere established in the living economy. The blood is sent by a
living engine, moving under laws peculiar to the state of life, into
living vessels, which in their turn acting under laws peculiar to the
state of life, so accommodate themselves to the current as absolutely
to offer no resistance to its progress; so accommodate themselves to
the moving power, as completely and everywhere to obviate the physical
impediments to motion inseparable from inorganic matter.

298. That the arterial tubes do possess and exert a truly vital power,
modifying the current of the blood they contain, is indubitably
established.

1. If in a living animal the trunk of an artery be laid bare, the mere
exposure of it to the atmospheric air causes it to contract to such a
degree, that its size becomes obviously and strikingly diminished. This
can result only from the exertion of a vital property, for no dead tube
is capable in such a manner of diminishing its diameter.

2. If during life an artery be opened and the animal be largely bled,
the arteries become progressively smaller and smaller as the quantity
of blood in the body diminishes. If the bleeding be continued until the
animal dies, and the arteries of the system be immediately examined,
they are found to be reduced to a very small size; if again examined
some time after death, they are found to have become larger, and they
go on growing successively larger and larger until they regain nearly
their original magnitude, which they retain until they are decomposed
by putrefaction.

3. M. Poiseuille distended with water the artery of an animal just
killed. This water was urged by the pressure of a given column of
mercury. The force of the reaction of the artery was now measured by
the height of a column of mercury which the water expelled from the
artery could support. It was found that the artery reacted with a
force greater than that employed to distend it, and greater than the
same artery could exert some time after death; but since mechanical
reaction can never be greater than the force previously exerted upon
it (293), it follows that the excess of the reaction indicated in this
case was vital.

4. If an artery be exposed and a mechanical or chemical stimulus be
applied to it, its diameter is altered, sometimes becoming larger and
sometimes smaller, according to the kind of agent employed.

299. Any one of these facts, taken by itself, affords a demonstration
that the arterial trunks and branches are capable of enlarging and
diminishing their diameter by virtue of a vital endowment. There is
complete evidence that the exertion of this vital power on the part
of the arterial trunk is not to communicate to the blood the smallest
impulsive force; the engine constructed for the express purpose of
working the current generates all the force that is required; but the
labour of the engine is economized by imparting to the tubes that
receive the stream a vital property, by which they wholly remove the
physical obstructions to its motion.

300. Driven by the heart through the arterial branches into the
capillaries, the blood courses along these minute vessels urged by the
same power. The most careful observers, from Haller and Spalanzani
down to the present time, concur in stating that the pulsatory
movement communicated by the heart to the blood in the great arteries
is distinctly visible under the microscope in the capillaries. "I
have often observed in frogs and tadpoles, and once in the bat," says
Wedemeyer, "that when the circulation was becoming feeble, the blood
in the finest capillaries advanced by jerks, corresponding with the
contractions of the heart. I remarked the same appearance in the fine
veins several times in the toad and tadpole, and once in the frog." If
an experimenter so dispose the circulation of the limb of an animal
that the flow of blood be confined to the branches of a single artery,
and a corresponding vein, it is found that the blood stagnates in the
vein whenever the current in the artery is stopped by a ligature, but
no sooner is the ligature removed from the artery, than the blood
begins again to flow freely along the vein, the capillaries of the
artery which have to send on the current to those of the vein being
now again within the influence of the heart. And if the impulse of
the heart be removed from the capillary system, by placing a ligature
around the aorta, the capillary circulation is uniformly and completely
stopped.

301. It was found by Dr. Hales, that, under ordinary circumstances,
the blood rises in a tube connected with a vein to the height only of
six inches, while it has been shown (290) that in the artery it ascends
as high as ten feet. This prodigious difference between the venous and
the arterial tension led to the conclusion that the impulsive force of
the heart was all but exhausted before the blood reached the veins, and
set physiologists on the search for other powers to carry on the venous
circulation. It was overlooked that the blood has an open and ready
escape from the great trunks of the veins through the right chambers of
the heart, and that in consequence of this free escape of their fluid,
these vessels indicate no greater tension than is just sufficient to
lift the blood to the heart, and to overcome friction[7]. M. Magendie
having laid bare the chief artery and vein of a living limb, and having
raised the vessels in such a manner that he could place a ligature
around the former, without including the latter, found that the flow
of blood from a puncture made below a ligature on the vein, was rapid
or slow, according as the heart was allowed to produce a greater or
less degree of tension in the artery, which tension was regulated by
compressing the artery between the fingers. After a similar preparation
of a limb, a ligature was placed around the vein; a tube was then
inserted into it; it was found that the blood ascended in the tube from
the obstructed vein just as high as from the artery.

302. Thus we are able to trace the action of the heart from the
beginning to the end of the circle. Of this circle it is the sole
moving power; but it is a living engine acting in combination with
living vessels. The force it exerts is a vital force, economized by the
agency of a vital property communicated to the vessels, by virtue of
which they spontaneously and completely remove all physical obstruction
to the progress of the stream through its channels.

303. Some German physiologists of great eminence, after a careful and
patient observation of the blood, have satisfied themselves that in
addition to the contraction of the heart, it is necessary to admit a
second original and independent motive force, namely, a self-moving
power inherent in the particles of the blood itself. The blood we
know is a living substance. No reason can be assigned why the power
of originating motion should not be communicated to such a substance
as well as to the muscular fibre, of which, indeed, one constituent
of the blood affords the basis. Such a power, if found to be inherent
in the particles of the blood, would explain some phenomena connected
with the circulation not yet clearly elucidated; but the proof of the
self-moving power of the blood does not yet seem to be complete. It
is, however, impossible to explain the phenomena of the circulation,
or to obtain a satisfactory view of some of the other functions of the
economy, without supposing the particles of the blood to be endowed
with a vital power of repulsion, in consequence of which they are
prevented from uniting when in contact, and the fluidity of the mass is
maintained.

In this account of the powers that move the blood, no notice has been
taken of the physical agents supposed to act as auxiliaries to the
heart, in carrying on the circulation, such as the suction power of the
thorax, and of the auricles of the heart, and the capillary attraction
of the vessels; because, without questioning the existence of such
agents, or denying that advantage may be taken of them, it seems pretty
clear that their influence is but trivial, and they assumed importance
only when the vital endowments of the tissues were not well understood.

304. The ultimate end for which the apparatus of the circulation is
constructed, and for which all its action is exerted, is to convey
arterial blood to the capillary arteries. These vessels are totally
distinct in structure and in office from the larger arterial tubes. All
the tunics of these minute vessels diminish in thickness and strength
as the tubes lessen in size, but more especially the middle or the
fibrous coat; which, according to Wedemeyer, may still be distinguished
by its colour in the transverse section of any vessel whose internal
diameter is not less than the tenth of a line; but that it entirely
disappears in vessels too small and too remote to receive the wave of
blood in a manifest jet. But while the membranous tunics diminish,
the nervous filaments distributed to them increase: the smaller and
thinner the capillary, the greater the proportionate quantity of its
nervous matter; and this is most manifest in organs of the greatest
irritability. The coats of the capillaries successively becoming
thinner and thinner, at length disappear altogether, and the vessels
ultimately terminate in membraneless canals formed in the substance of
the tissues. "The blood in the finest capillaries," says Wedemeyer,
"no longer flows within actual vessels; it is not contained in tubes
whose parietes are formed by a membranous substance distinguishable by
its texture and compactness from the adjoining cellular tissue: it is
contained in the different tissues in channels which it forms in them
for itself; and, under the microscope, the stream is seen easily and
rapidly to work out for itself a new passage in the tissues which it
penetrates."

305. Some of these fine capillaries, before they entirely lose their
membranous tunics, communicate directly with veins. Of the capillaries
which terminate by direct communication with veins, some are large
enough to admit of three or four of the red particles of the blood
abreast; the diameter of others is sufficient to admit only of one;
while others are so small that they can transmit nothing but the serum
of the blood. As long as the capillary is of sufficient magnitude
to receive three or four of the particles abreast, it is evident
that it possesses regular parietes; but by far the greater number,
before they communicate with veins, lose altogether their membranous
coats. There are no visible openings or pores in the sides or ends
of the capillaries by means of which the blood can be extravasated,
preparatory to its being imbibed by the veins. There is nowhere
apparent a sudden passage of the arterial into the venous stream; no
abrupt boundary between the division of the two systems. The arterial
streamlet winds through long routes, and describes numerous turns
before it assumes the nature and takes the direction of a venous
streamlet. The ultimate capillary rarely passes from a large arterial
into a large venous branch.

306. The vital power which it has been shown (298) is possessed by
the arterial trunks and branches, is still more intense in the minute
capillaries. If alcohol, strong acetic acid, naphtha, and other
stimulating fluids, be injected into the arteries of a living animal,
it is found that they are not transmitted through the capillaries
at all, or, at all events, that they make their way through them
with extreme difficulty; whereas mild, unirritating fluids pass with
rapidity and ease. Wedemeyer exposed and divided the main artery in
the fore-leg of a horse, together with the corresponding vein in the
shoulder. Several syringes-full of tepid water were now injected into
the lower end of the artery. The gentlest pressure was sufficient to
force the fluid through the capillaries. At each injection the water
issued in a full stream from the aperture of the vein, the flow of the
fluid ceasing as soon as the injection was stopped. Next, instead of
water, four syringes-full of pure cold brandy were injected. To propel
this fluid through the capillaries, so as to render its smell and taste
perceptible at the aperture of the vein, required a great degree of
pressure; and when at last the fluid issued from the vein, it merely
trickled in a feeble stream.

The experiment being repeated on another horse with vinegar, six
syringes-full of which being injected in rapid succession, at first
this fluid passed as easily as water, afterwards it flowed with greater
difficulty and in a small stream; before long the force required to
propel it was extreme, and at last the obstruction to its passage
became complete, so that no fluid whatever issued from the vein.

These experiments, whenever repeated, afforded the same result, and
they demonstrate that the capillaries are capable of being stimulated
to contract upon their contents, and that they can contract with such
force as to stop the current. It is manifest that the power by which
they do this is vital, because after death all fluids, the mildest and
the most acrid, pass through them with equal facility.

307. Drs. Thompson, Philip, Hastings, and others in this country,
have applied stimulants of various kinds to the capillary arteries,
in order to observe with the microscope the changes which the vessels
undergo. The results of these experiments, performed independently,
agree with each other; and all the observers concur in stating that
those results are so obvious and decisive as to admit of no question.
Wedemeyer, fully aware of all that had been done on this subject by
the English physiologists, repeated their experiments with his usual
patience and care, vigilantly watching the effects with his microscope.
His observations completely coincide with those of our countrymen. The
circulation being observed in the mesentery of the frog and in the web
of its foot, it was apparent that no change whatever took place in
the diameter of the small arteries, nor in that of the capillaries,
as long as the circulation was allowed to go on in its natural state;
but as soon as stimulants were applied to them, an alteration of their
diameter was visible. Alcohol, without much apparent contraction of the
vessels, stopped the flow of the blood. Muriate of soda, in the course
of three or four minutes, caused the vessels to contract one-fifth of
their calibre, which contraction was followed by dilatation and gradual
retardation and stoppage of the blood. Ammonia caused immediate and
direct dilatation, and the effect of galvanism was still more striking.
In a space of time varying from ten to thirty seconds, nay, sometimes
immediately after the completion of the galvanic circle, the vessels
contracted, some a fourth, others half, and others three-fourths, of
their calibre. The flow of the blood through the contracted vessels
was accelerated. The contraction sometimes lasted a considerable time,
occasionally several hours; in other instances the contraction ceased
in ten minutes, and the vessels resumed their natural diameter. A
second application of galvanism to the same capillaries seldom caused
any material contraction.

308. The evidence, then, is abundant that stimulants are capable of
modifying to a great extent the action of the capillary arteries,
sometimes causing them to contract, at other times to dilate; sometimes
quickening the flow of blood through them, at other times retarding it,
and frequently altogether arresting its motion. This contractile power
of the capillaries must be a vital endowment, for no such property is
possessed by any substance destitute of life, and there is satisfactory
evidence that it is communicated, regulated, and controlled by the
organic nerves, which, as has been shown, increase as the size of the
vessels and the thickness of their membranous tunics diminish. The
powerful influence of these nerves upon the capillary vessels is placed
beyond doubt or controversy by the obvious local changes produced in
the capillary circulation by sudden, and even by mental, impressions,
by the flush of the cheek and the sparkle of the eye, at a thought
conceived or a sound heard; changes which can be effected, as far as we
have any knowledge, by no medium excepting that of the nerves. The part
performed by electricity, the physical agent by which it is conceived
the nerves operate, will be considered hereafter.

309. Exerting upon each other a vital force of repulsion, under a
vital influence derived from the organic nerves, urged by the vital
contraction of the heart, the particles of the blood reach the extreme
capillaries. Most of these capillaries terminate (304) in canals, which
they work out for themselves in the substance of the tissues. The
tissues are endowed with a vital attractive force, which they exert
upon the blood—an elective as well as an attractive force: for in
every part of the body, in the brain, the heart, the lung, the muscle,
the membrane, the bone, each tissue attracts only those constituents
of which it is itself composed. Thus the common current, rich in all
the proximate constituents of the tissues, flows out to each. As the
current approaches the tissue, the particles appropriate to the tissue
feel its attractive force, obey it, quit the stream, mingle with the
substance of the tissue, become identified with it, and are changed
into its own true and proper nature. Meantime, the particles which are
not appropriate to that particular tissue, not being attracted by it,
do not quit the current, but passing on, are borne by other capillaries
to other tissues, to which they are appropriate, and by which they
are apprehended and assimilated, When it has given to the tissues the
constituents with which it abounded, and received from them particles
no longer useful, and which would become noxious, the blood flows into
the veins to be returned by the pulmonic heart to the lung, where,
parting with the useless and noxious matter it has accumulated, and,
replenished with new proximate principles, it returns to the systemic
heart, by which it is again sent back to the tissues.

310. Particles of blood are seen to quit the current and mingle with
the tissues; particles are seen to quit the tissues and mingle with
the current. But all that we can see, with the best aid we can get,
does but bring us to the confines of the grand operations that go on,
of which we are altogether ignorant. Arterial blood is conveyed by
the arteries to the capillaries; but before it has passed from under
the influence of the capillaries it has ceased to be arterial blood.
Arterial blood is conveyed by the carotid artery to the brain; but
the cerebral capillaries do not deposit blood, but brain. Arterial
blood is conveyed by its nutrient arteries to bone, but the osseous
capillaries do not deposit blood, but bone. Arterial blood is conveyed
by the muscular arteries to muscle, but the muscular capillaries do not
deposit blood, but muscle. The blood conveyed by the capillaries of
brain, bone, and muscle is the same, all comes alike from the systemic
heart, and is alike conveyed to all tissues; yet in the one it becomes
brain, in the other bone, and in the third muscle. Out of one and the
same fluid these living chemists manufacture cuticle, and membrane, and
muscle, and brain, and bone; the tears, the wax, the fat, the saliva,
the gastric juice, the milk, the bile, all the fluids, and all the
solids of the body.

311. And they do still more; for they are architects as well as
chemists; after they have manufactured the tissue, they construct the
organ. The capillaries of the eye not only form its different membranes
and humours, but arrange them in such a manner as to constitute the
optical instrument; and the capillaries of the brain not only form
cerebral matter, but build it up into the instrument of sensation,
thought, and motion.

312. The practical applications of these phenomena are numerous and
most important; but they can be clearly and impressively stated
only when the operation of the physical agents which influence the
circulation, and which proportionally affect life and health, has been
explained.




FOOTNOTES.


[1] Computationi in alimentis faciendæ hanc formam esse Ulpianus
scribit, ut _à primâ ætate_ usque ad annum vicesimum quantitas
alimentorum triginta annorum computetur, ejusque quantitatis Falcidia
præstetur: _ab annis verò viginti_ usque ad annum vicesimumquintum
annorum viginti octo: _ab annis vigintiquinque_ usque ad annos
triginta, annorum vigintiquinque: _ab annis triginta_ usque ad annos
trigintaquinque annorum viginti duo; _ab annis trigintaquinque_
usque ad annos quadraginta annorum viginti: _ab annis quadraginta_
usque ad annos quinquaginta tot annorum computatio fit quot ætate
ejus ad annum sexagesimum deerit, remisso uno anno: _ab anno verò
quinquagesimo_ usque ad annum quinquagesimumquintum annorum novem:
_ab annis quinquagintaquinque_ usque ad annum sexagesimum annorum
septem: _ab annis sexaginta_, cujuscunque ætatis sit, annorum quinque;
eoque nos jure uti Ulpianus ait, et circa compu tationem ususfructus
faciendam. Solitum est tamen _à primâ ætate_ usque ad annum trigesimum
computationem annorum triginta fieri: _ab annis verò triginta_ tot
annorum computationem inire, quot ad annum sexagesimum deesse videntur;
nunquam ergo amplius quam triginta aunorum computatio initur. Sic
denique, et si Reipublicæ ususfructus egetur, sive simpliciter, sive
ad ludos, triginta annorum computatio fit. Si quis ex heredibus rem
propriam esse contendat, deinde hereditariam esse convincatur: quidem
putant ejus quoque Falcidiam non posse retineri; quià nihil intersit,
subtraxerit an hereditariam esse negaverit. Quod Ulpianus rectè
improbat. (Vide Justin. Pandect. lib. 35, tit. 2, ad Legem Falcidiam.)

[2] Which maximum is a little above the highest point hitherto any
where attained.

[3] Hence in the preparation of jelly as an article of diet, the parts
of young animals, as the feet of the calf, are principally employed;
whereas soups made from beef contain a large proportion of albumen,
while in those made from veal the proportion of jelly preponderates.

[4] Treatise on Ligaments, by Bransby B. Cooper, Esq.

[5] For these illustrations I am indebted to Mr. Lister, who has been
so kind as to make drawings of the objects for me.

[6] Whenever there is any interruption to the ordinary flow of the
circulating fluids, the powers of the anastomosing circulation are
capable of being increased to a surprising extent. The aorta itself
has frequently been tied in animals of considerable size without
destroying life; in the human body it has also been found obliterated
by disease in different parts of its course, in one case as high
as the termination of its curvature. In the cure for aneurism the
external iliac artery has been tied by Mr. Abernethy with success; the
subclavian artery below the clavicle by Mr. Keate; the common carotid
by Sir Astley Cooper; the subclavian artery above the clavicle by
Mr. Ramsden; the internal iliac artery by Dr. Stevens; the arteria
innominata by Dr. Mott, of New York; and lastly, the abdominal aorta
itself, by Sir A. Cooper. Mr. Grainger tied the abdominal aorta of a
dog; when the animal had recovered from that operation, the carotids
and the great trunks of the anterior extremities were tied: in this
manner the whole course of the circulation was altered. The dog, which
was of very large size, survived all these operations, and appeared to
enjoy its ordinary health. Grainger's General Anatomy, p. 251-253.

[7] See this matter very ably discussed in Dr. Arnott's excellent work
on the Elements of Physics, vol. i.


END OF VOL. I.


London: Printed by W. CLOWES and SONS, Stamford Street.




TRANSCRIBER'S NOTES.
1. (Figure LXXIV.) was incorrectly labeled as (Figure LXXVI.).
     This has been corrected.
2. No Figure LXX in original book.







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