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Title: Treatise on the Anatomy and Physiology of the Mucous Membranes

Author: Xavier Bichat

Translator: Joseph Houlton

Release date: September 5, 2016 [eBook #52987]

Language: English

Credits: Produced by Sonya Schermann, John Campbell and the Online
        Distributed Proofreading Team at http://www.pgdp.net (This
        file was produced from images generously made available
        by The Internet Archive)


*** START OF THE PROJECT GUTENBERG EBOOK TREATISE ON THE ANATOMY AND PHYSIOLOGY OF THE MUCOUS MEMBRANES ***




Produced by Sonya Schermann, John Campbell 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_.

  Obvious typographical errors and punctuation errors have been
  corrected after careful comparison with other occurrences within
  the text and consultation of external sources.

  More detail can be found at the end of the book.




  A

  TREATISE

  ON

  THE ANATOMY AND PHYSIOLOGY

  OF THE

  Mucous Membranes;

  WITH

  ILLUSTRATIVE PATHOLOGICAL OBSERVATIONS.


  _From the French_

  OF

  XAVIER BICHAT.


  BY JOSEPH HOULTON,

  MEMBER OF THE ROYAL COLLEGE OF SURGEONS IN LONDON.


  LONDON:

  PRINTED FOR J. CALLOW,

  Medical Library,

  16, PRINCES STREET, CORNER OF GERRARD STREET, SOHO.

  MDCCCXXI.




CHARLES WOOD, Printer,

Poppin's Court, Fleet Street, London.




THE

TRANSLATOR'S PREFACE.


The works of no medical writer deserve a more attentive perusal
than those of the illustrious BICHAT. Erudite, observant, and
industrious, he, at an early age, reared a monument of science,
which will perpetuate his name and matchless talents. From the
rich treasures he has left, the Translator presumes to present
this Treatise in an English costume. Where all is excellent it
is difficult to make a satisfactory selection; yet this portion
of the author's productions merits the particular attention of
medical students and practitioners in general, as it leads to the
knowledge of the structure and economy of that part of the animal
organization, which, more than any other, is subject to morbid
affections.

The aim of the Translator has been faithfulness, clearness, and
conciseness, rather than elegance: how he has fulfilled his
intention he must leave to the decision of the candid Reader.

  SAFFRON WALDEN,
  JULY 1, 1821.




CONTENTS.


  SECT.                                                             PAGE

     I. _Of the Situation and Number of Mucous Membranes_              1

    II. _Of the Exterior Organization of Mucous Membranes_             9

   III. _Of the Interior Organization of Mucous Membranes_            20

    IV. _Of the Glands of Mucous Membranes_                           37

     V. _Of the Vascular System of Mucous Membranes_                  54

    VI. _Of the Variations in the Organization of Mucous Membranes_   64

   VII. _Of the Vital Powers of Mucous Membranes_                     70

  VIII. _Of the Sympathies of Mucous Membranes_                       81

    IX. _Of the Functions of Mucous Membranes_                        85

     X. _Remarks on the Affections of Mucous Membranes_               98




A

TREATISE

ON

MUCOUS MEMBRANES.




SECTION I.

OF THE SITUATION AND NUMBER OF MUCOUS MEMBRANES.


1. The Mucous Membranes occupy the interior of those cavities,
which, by various openings, communicate with the skin. Their
number, at the first view, appears very considerable; for the
organs within which they are reflected are numerous. The stomach,
bladder, urethra, uterus, ureters, the intestines, &c., borrow from
these membranes a part of their structure: nevertheless, if it be
considered, that they are continuous throughout, that everywhere
they are observed to be extended from one organ to others, arising,
as they did at first, from the skin, their number will appear to
be singularly limited. In fact, in thus contemplating them, not as
insulated in each part, but as continued over various organs, it
will appear that they are reducible to two general surfaces.

2. The first of these two surfaces, entering by the mouth, nose,
and anterior surface of the eye, (1) lines the first and second
of these cavities: from the first it extends into the excretory
ducts of the parotid and submaxillary glands; from the other it is
continued into all the sinuses, it forms the tunica conjunctiva,
descends by the puncta lacrymalia through the canal and lacrymal
sac to the nose. (2) It descends into the pharynx, and there
furnishes the inner surface of the Eustachian tube, and thence
it penetrates and lines the internal ear. (3) It sinks into the
trachea, and spreads itself over all the air passages. (4) It
enters the œsophagus and stomach. (5) It extends into the duodenum,
where it furnishes two branches, one destined to the ductus
communis choledochus, to the numerous rami of the hepatic duct, to
the cystic duct and gall bladder; the other to the pancreatic duct
and its various ramifications. (6) It is continued into the small
and large intestines, and finally terminates at the anus, where it
is identified with the skin.

3. The second general mucous membrane enters, in men, by the
urethra, and thence spreads from one part through the bladder,
ureters, pelves, calices, papillæ, and uriniferous tubes; from the
other it sinks into the excretory ducts of the prostate gland,
into the ejaculatory ducts, the vesicula seminales, the vassa
defferentia, and the infinitely convoluted branches from which they
arise. In women, this membrane enters by the vulva, and from one
part penetrates the urethra, and is distributed, as in men, through
the urinary organs; from the other part it extends into the vagina,
which it lines, as it also does the uterus and the fallopian tubes,
and through the apertures at the extremities of these ducts it
comes in contact with the peritoneum. This is the only example
in the economy, of a communication between the mucous and serous
surfaces.

4. This manner of describing the track of the mucous surfaces by
saying that they extend, sink, penetrate, &c., from one cavity
to another, is certainly not conformable to the march of nature,
which forms in each organ the membranes that belong to it, and
does not thus extend them from one to the other; but our manner
of conceiving is best accommodated by this language, of which the
least reflection will rectify the sense.

5. In thus bringing all the mucous surfaces to two general
membranes, I am supported, not only by anatomical inspection,
but pathological observation also furnishes me with lines of
demarcation between the two, and with points of contact between
the different portions of the membranes of which each is the
assemblage. In the various sketches of epidemic catarrhs made
by authors, we frequently see one of these membranes has been
affected throughout its extent, whilst the other, on the contrary,
has remained untouched. It is not uncommon to observe a general
affection of the first, _viz._ that which extends from the mouth,
nose, and anterior surface of the eye, into the alimentary canal
and bronchi. The last epidemic observed at Paris, with which M.
Pinel was himself affected, bore this character: that of 1761,
described by Rayons, presented the same feature: that of 1732,
described in the Memoirs of the Edinburgh Society, was remarkable
for a like phenomenon. Now we do not see at the same time a
corresponding affection in the mucous membrane which spreads over
the organs of urine and of generation. Here is, therefore, (1)
an analogy between the different portions of the first, by the
uniformity of the affection; (2) a line of demarcation between
them, by the healthy state of the one and the disease of the other.

6. We observe also, that irritation on any one point of these
membranes frequently produces a pain in another point of the same
membrane, which is not irritated; thus a stone in the bladder
causes a pain at the end of the glans, worms in the intestines
produce an itching at the nose, &c. &c. Now in these phenomena,
which are purely sympathetic, it is extremely rare that the partial
irritation of one of these two membranes produces a painful
affection in a part of the other.

7. We ought, therefore, from inspection and observation, to
consider the mucous surface in general as formed by two grand
membranes, spread over several organs, and having no communication
with each other but by the skin, which is intermediate, and which,
being continuous with both, thus concurs with them to form a
general membrane, entire throughout, enveloping the exterior of the
animal, and extending to the interior over most of its essential
parts. It should seem, that there exists important relations
between the internal and external portions of this unique membrane,
and this we shall soon be shown by ulterior researches.




SECTION II.

OF THE EXTERIOR ORGANIZATION OF MUCOUS MEMBRANES.


8. Every mucous membrane presents two surfaces; the one adhering
to the adjacent organs; the other free, beset with villosities,
and always moist with a mucous fluid: each of them deserves a
particular attention.

9. The adherent surface is attached to muscles almost throughout
its extent. The mouth, the pharynx, the whole of the alimentary
canal, the bladder, the vagina, the uterus, and part of the
urethra, &c. present a muscular bed, embracing the exterior of
their mucous coat. In animals that have the panniculus carnosus,
this disposition perfectly coincides with that of the skin, which,
as we shall see, is in other respects analogous in structure
to mucous membranes. In man the cutaneous organ presents here
and there traces of this exterior muscle, as we observe in the
platysma myoides, the palmaris brevis, the occipito frontalis, in
most of the muscles of the face, &c. This disposition of mucous
membranes places them under the influence of those habitual changes
of contraction and dilatation, which are favourable to their
secretion, and various other functions.

10. This muscular bed is not immediately inserted into the exterior
surface of the mucous membranes, but rather, according to Albinus,
into a dense layer of cellular tissue, which all the ancient
authors have denominated, in the stomach, intestines, and bladder,
the nervous coat; but when well examined it presents no character
analogous to that which the name indicates. The experiment of
inflation, by which it is brought into its primitive state, is not
so easy as Albinus and others have pretended; which led me to think
that its nature might not be cellular, but that it was probably
of a fibrous texture, formed by a web of extremely delicate and
scarcely visible tendons, offering points of origin and insertion
to all the fleshy fibres of the muscular bed, which, as we know,
never describe entire circles, but rather different segments of
that curve. I confess that this conjecture, though very likely, is
not founded upon any decisive and rigorous experiment.

11. Whatever may be the nature of this intermediate membrane to
the mucous and muscular coats, it evidently has a dense, close
texture, which gives it a resistance very analogous to one of the
fibrous membranes. It is from this that the organ receives its
form; it is this which maintains and controls its shape, as may be
proved by the following experiment. Take a portion of intestine:
remove in any part of the bowel a part of this membrane, with the
serous and muscular membranes: having applied a ligature to the
inferior end, inflate it, the air will produce in the denuded part
an hernia of the mucous coat. Take another portion of intestine,
turn it, dissect off a small part of the mucous membrane and of
this coat: inflation will produce upon the serous and muscular
coats the same phenomenon as in the preceding case it did in the
mucous membrane. It is therefore to this intermediate tunic that
the mucous membrane owes its power of resistance to substances
which distend it. This applies equally to the stomach, bladder,
œsophagus, &c.

12. The free surface of mucous membranes, or that which is
continually moistened by the fluid from which they borrow their
name, presents two kinds of wrinkles or folds, the one inherent
in their structure and which is constantly present, whatever may
be their state of contraction or dilatation, such as the pylorus,
the valvula conniventes, the valve of the colon, &c. These folds
are formed, not merely by the mucous membranes, but also by the
intermediate membrane mentioned above, and which in these parts
takes a remarkable density and thickness.

13. The other folds may be called accidental, and are only observed
during the contraction of the organ; such are those of the inner
surface of the stomach, and of the large intestines, &c. In most
of the human subjects brought to our amphitheatres, these folds in
the stomach, of which so much has been said, are not perceptible,
because generally the subject has died of a disease which has
impaired the vital powers, without preventing all the action of
this viscus; so that, although it is frequently found empty, its
fibres are not in the least contracted.

14. In experiments on living animals, on the contrary, these folds
are very apparent; and observe how they may be demonstrated.
Let a dog eat or drink copiously; open it immediately, and make
an incision into the stomach the whole length of its greater
curvature, no fold will then appear, but it soon contracts, its
edges are drawn in, and the whole of the mucous surface is covered
with numerous prominent plicæ in the form of circumvolutions. The
same result may be observed in the stomach of a recently killed
animal by distending it with air, and then opening it; or, what is
still better, by laying it open whilst empty, and stretching it,
the folds will disappear, and when we cease to make the extension
they immediately form again and are very apparent.

15. I would observe on the subject of inflating the stomach, that
by distending it with oxygen gas the application of this fluid
does not produce more prominent folds, and therefore no stronger
contraction, than when carbonic acid gas is used for the same
purpose. This experiment presents a result very similar to what
I have observed when I have rendered animals emphysematous by
different æriform fluids. Frogs and Guinea pigs (these are the two
kinds I have chosen, the one being an animal of red and cold, and
the other of red and warm blood) presented very little difference
in their irritability, or their Galvanic susceptibility, whether
inflated with oxygen gas or with carbonic acid gas. They live very
well with this artificial emphysema, which gradually disappears.
Inflation with nitrous gas is always mortal, and its contact
appears to strike the muscles with atony. The stomach distended
with it very soon loses its power of contracting, and its folds
disappear. Here, as in all the experiments which have the vital
powers for their object, we frequently obtain very variable results.

16. It follows, from what we have said respecting the folds of
mucous membranes, that in the contraction of the hollow organs,
which are lined by them, they suffer but a very trifling diminution
of surface, they scarcely contract at all, but fold themselves
within; so that in dissecting them upon their contracted organ, we
have an extent of surface nearly equal to that which they present
during its dilatation. This assertion, which is true concerning
the stomach, the œsophagus, and the intestines, is, perhaps, not
quite so as respects the bladder, whose contraction does not show
within such prominent folds, but they are sufficiently marked to
bring the mucous membrane of this organ under the general law.
It is, also, nearly the same with the gall bladder; yet we find
here another cause; observed alternately, in a state of hunger and
during digestion, it will be found to contain double the quantity
of bile in the former case that it does in the latter, as I have
had the opportunity of seeing in numerous instances, in experiments
made with this object in view, or with other intentions. Now, when
it has evacuated part of its contents it does not contract upon
the remainder of the bile, with the energy of the stomach when it
contains but little food, nor with the power of the bladder when
it contains but a small quantity of urine, but is then flaccid,
so that its distention or nondistention has but very trifling
influence upon the folds of its mucous membranes.

17. Moreover, in saying that the mucous membranes present with
trifling variation the same extent of surface in the dilatations
as during the contraction of their respective organs, I intend to
speak of the ordinary state of the functions only, and not of those
enormous dilatations which are frequently seen in the stomach and
bladder, more rarely in the intestines. In such cases there is
doubtless a real extension, which in the membrane coincides with
that of the organ.

18. One remarkable observation that the free surface of mucous
membranes affords us, and which I have already pointed out,
is, that this face is everywhere in contact with bodies of a
different nature to that of the animal: these bodies are either
introduced from without for its nourishment, and are not yet
assimilated to its substance, as we see in the alimentary canal
and in the trachea, or they are produced within, as we observe in
the excretory ducts of the glands, which all open into cavities
lined by mucous membranes, and discharge those particles, which,
after having for some time formed a part of the composition of
the solids, become heterogeneous to them, and are thrown off
by that habitual action of decomposition, which takes place in
living bodies. According to this observation we must consider the
mucous membranes as defensive coats, placed between our organs and
foreign bodies, and that they consequently serve the same purpose
internally which the skin does externally, as respects bodies that
are in contact with it.




SECTION III.

OF THE INTERIOR ORGANIZATION OF MUCOUS MEMBRANES.


19. Between the mucous and other membranes, as respects their
interior organization, there is this essential difference, that
they are always formed by several thin fibrous layers; these layers
or coats are, with the exception of the rete mucosum, the same as
those which compose the skin with which these membranes have the
most exact analogy. We are about to examine separately each of
these layers, which are the epidermis, the corps papillaire, and
the chorion, in their general attributes; we shall afterwards
consider the particular modifications which they undergo in the
different parts of the mucous surfaces.

20. All authors have admitted the epidermis of mucous membranes:
it appears, even, that the greatest part of them have believed
that it is merely that portion of the skin which descends into the
cavities to line them; Haller in particular is of this opinion; but
the least inspection is sufficient to show, that here, as in the
skin, it forms but a layer superficial to the corps papillaire and
chorion; boiling water, which detaches it from the surface of the
palate, the tongue, and even from the pharynx, leaves the two other
coats denuded and apparent.

21. This epidermis is very distinct upon the glans, at the anus, at
the orifice of the urethra, at the entrances of the nasal fossæ,
and of the mouth, and in general wherever the mucous membranes
arise from the skin. It is demonstrated in these different places
by the frequent excoriations which occur on them; it may be raised
from the lips by a very fine lancet by the action of boiling water,
a hot iron, or even by epispastics, as the method of the ancients
proves, who employed them to produce a fresh raw surface for the
cure of the hare lip.

22. But in proportion as we go into the depth of the mucous
membranes, the existence of this coat becomes more difficult to be
demonstrated; it cannot be raised by the finest instrument, nor
detached by boiling water, at least in the gall bladder, in the
stomach, and intestines. I have made these experiments in fresh
slain animals, and also in those where the natural heat had quite
left them. But what our experiments cannot effect, inflammations
will often produce. All the authors, who have written on the
affections of the organs which are lined by these membranes,
mention instances in which flakes, more or less considerable, have
been voided by the urethra, anus, mouth, nostrils, &c. Haller has
collected a great number of similar observations. Without doubt
the separation of the epidermis in these cases is produced nearly
in the same way as we observe it in cutaneous inflammations. In
many subjects that have died with symptoms of inflammation of the
mucous membranes, and which I have already had the opportunity of
dissecting, or of seeing dissected, I have not yet been able to
observe this separation going on; that is to say, the epidermis
separated at one point, and still remaining adherent at others, as
in erysipelas. I have tried in vain to produce this effect by the
application of an epispastic to the inner surface of the intestines
of a dog.

23. This epidermis is subject, like that of the skin, to become
callous by pressure. Choppart cites a case of a shepherd, "dont
le canal de l'urètre présentoit cette disposition, à la suite de
l'introduction fréquemment répétée d'une petite baguette pour se
procurer des jouissances voluptueuses." We know the density that
this envelope takes in the stomachs of the gallinacea. In certain
circumstances, where the mucous membranes are protruded from
the body, as in prolapsus ani, inversion of the vagina, in the
artificial anus, &c., sometimes the pressure of the dress produces
in this epidermis a thickness evidently more considerable than is
natural to it.

24. The epidermis is attached to the hair on the skin, although
it does not afford its immediate origin; sometimes also piliform
productions are observed in the mucous membranes. The bladder, the
stomach, the intestines, and the pituitary membrane have been in
various instances the seat of these unnatural excrescences: Haller
has cited various instances of them.

25. This envelope appears to have upon the mucous surfaces the
same texture as on the skin, excepting in the delicacy of the
laminæ from which it is produced. It is to this delicacy, which
gives more exposure to the nerves, that we must doubtless refer
the facility with which we excite various remarkable modifications
in the sensibility, when by the Galvanic process we apply zinc to
the mucous surface of the conjunctiva, the pituitary membrane, the
internal membrane of the rectum, or of the gums, &c., and bring
these several metal plates into mediate or immediate contact. The
epidermis when removed is quickly reproduced; being destitute
of all kinds of sensibility, it in this respect serves the same
purpose as the skin, by guarding the very sensible corps papillaire
which is subjacent to it. To its presence over the mucous membranes
we must attribute the ability they have of being exposed to the
air, and even to the contact of foreign bodies, without excoriating
or inflaming, as is seen in cases of artificial anus, prolapsus
ani, &c., whilst serous and fibrous membranes never suffer such
exposure with impunity. Hence there is no danger, in this respect,
from opening the bladder: hence, on the contrary, that precept so
justly recommended, not to open the cavity of the peritoneum, and
to make the least possible incision into the synovial capsules.
I would observe, that the existence of the epidermis upon mucous
membranes is an important consideration, as respects the opinion
of those who, like Séguin, believing them to be without it, have
said, that contagion is always received by the lungs, and not by
the skin, which is, according to them, defended by this envelope.

26. In the organization of the skin, immediately under the
epidermis is placed the corpus mucosum, particularly described by
Malpighi, and generally considered as the seat of colour in the
different varieties of the human species. It is described as a
coat, pierced with holes by the passage of the nervous papillæ: M.
Sabattier points out the manner of demonstrating it. Sömmering has,
it is said, seen it separated from the epidermis and chorion on the
scrotum of an Ethiopian. I confess that I have not yet been able to
perceive it: M. Portal does not appear to have been more fortunate.

27. We distinguish only a kind of gelatinous juice intermediate
to the corps papillaire and epidermis, and most commonly it is
not even apparent; I have never been able to observe more with
certainty. In examining the skin of a Negro with attention, the
epidermis being detached, I have seen the external surface of the
chorion tinged with black, and that was all. Further, whatever
this corpus mucosum may be, it certainly does not exist in mucous
membranes, since they do not participate in the colour of the
integuments. The heat of the sun, which darkens these in white
people, does not appear to act upon the commencement of these
membranes, which are equally exposed with them to its influence,
as is seen in the red borders of the lips, &c. Nevertheless, I
have many times remarked on the palates of dogs, which have been
the subjects of my experiments, similar spots to those which have
marked their skin.

28. The sensibility of the skin is principally owing to the corps
papillaire; that of the mucous membranes, exactly analogous to
that of the skin, appears to me to arise from the same cause. The
nervous papillæ of these membranes cannot be questioned: at their
origin, where they dip into the cavities, even in the commencement
of these cavities, as on the tongue, the palate, the internal
surface of the alæ nasi, on the glans, in the fossa naviculare,
on the inside of the lips, &c., inspection is sufficient to
demonstrate them. But, we ask, do these papillæ exist also in those
parts of mucous membranes which are more remote from the surface of
the body? Analogy answers in the affirmative, since sensibility is
the same there as at their origin; but inspection proves it in a
no less certain manner. I believe, that the villosities with which
we see them everywhere thickly furnished are nothing else than
these papillæ.

29. Very different notions have been entertained concerning the
nature of these villosities: they have been considered, in the
œsophagus and in the stomach, as destined to the exhalation of the
gastric juice, in the intestines as serving for the absorption of
chyle, &c. But (1) It is difficult to conceive how an organ, so
nearly similar throughout its extent, should fulfil, in different
parts, such different functions; I say so nearly similar, because
we know, that the villosities of the small are more prominent than
those of the large intestines. (2) What would be the functions of
the villosities of the pituitary membrane, of the internal coat
of the urethra, and of the bladder, if they had no connection
with the sensibility of these membranes. (3) The microscopic
experiments so boasted of by Leiberkuhn, on the erection of the
intestinal villosities, have been contradicted by those of Hunter
and Cruikshank, and, above all, by those of Hewson. I can assert,
that I have never seen any thing of the kind on the surface of
the small intestines during the absorption of chyle, and yet it
appears to be a thing that cannot vary in different examinations.
(4) It is true that these intestinal villosities are everywhere
accompanied by a vascular web, which gives them a colour very
different from that of the cutaneous papillæ; but the nonappearance
of the cutaneous web is occasioned only by atmospherical pressure,
by means of the contraction that it produces in the minute vessels:
see, for instance, the newly-born infant; its cutaneous surface is
as red as that of its mucous membranes, and if the papillæ were a
little more elongated the skin would exactly resemble the internal
surface of the intestines: moreover, who does not know, that the
vascular web surrounding the papillæ is rendered so apparent by
fine injections as entirely to change the colour of the skin?

30. That in the stomach this vascular web exhales the gastric
juice, and in the intestines it is interlaced with the origin of
the absorbents, so that they embrace the villosities, are facts
that we must admit, after the experiments and observations of the
anatomists, who in these times have been engaged with the lymphatic
system: but that does not contradict the assertion, that the bases
of these villosities are nervous, and perform the same functions
only on the mucous membrane as the papillæ do on the cutaneous
organ. This view of them, by explaining their existence as observed
generally over all the mucous surfaces, appears to me much more
conformable to the plan of nature than to suppose that they
perform, in their different parts, diverse and frequently opposite
functions.

31. However, it is difficult to decide the question by ocular
observation; the tenuity of these prolongations conceals their
structure even from our microscopic instruments, a kind of agents
by which physiology and anatomy do not appear to me in other
respects ever to have obtained great assistance, because when parts
are so viewed each person sees in his own way, and is impressed
accordingly. It is therefore the observing of the vital functions
that should above all guide us. Now by judging of the villosities
in this way it appears evident, that they have the nature which
I have attributed to them. The following experiment will serve
to demonstrate the influence of the corps papillaire upon the
cutaneous sensibility: it succeeds also with mucous membranes.
If we remove any part of the epidermis, and irritate the corps
papillaire with a pointed instrument, the animal writhes, cries,
and gives signs of acute pain. If afterwards the cutis be pierced,
and with the instrument the internal surface of the chorion be
irritated, the animal will not appear to suffer pain, unless by
accident some nervous filaments should be touched. Thence it
follows very evidently, that the sensibility of the skin resides
in its external surface, that the nerves pass through the chorion
without being interwoven with its texture, and that their diffusion
only takes place on the corps papillaire. It is the same in mucous
surfaces.

32. The length and form of the villosities vary in the different
mucous surfaces. Their appearance is not the same in the stomach,
the intestines, the bladder, the gall bladder, on the glans, &c.
which variation exactly coincides with the sensibility peculiar to
each organ, a sensibility proved by numerous observations since
Bordeu, who was the first to direct the attention of physiologists
to the particular modifications that this property undergoes in the
different parts.

33. Like the skin, the mucous membranes have their chorion: it is
thick on the palate, gums, and pituitary membrane, delicate in the
stomach and intestines, not very distinct in the bladder, gall
bladder, and excretory ducts. It appears to be formed of condensed
cellular strata, strongly united, as in the skin. Maceration
develops this texture in a very sensible manner. There is
nevertheless this difference, that in dropsy the cutaneous chorion
rises and resolves itself into distinct cellules, that become
filled with water, whilst no such change takes place in the mucous
chorion under similar circumstances. Does this difference in the
morbid state suppose a dissimilarity of structure? Certainly not;
for the synovial membrane is evidently of the same nature as the
serous membranes; and nevertheless it does not participate in the
hydropic diathesis which often affects them universally. It would
be curious to expose mucous membranes to the action of tan, to see
if they would present the same phenomena as the skin.




SECTION IV.

OF THE GLANDS OF MUCOUS MEMBRANES.


34. Besides the three strata, which we have just mentioned, the
mucous membranes present in their structure a great number of
glands and blood vessels. The mucous glands exist in all membranes
which bear that appellation: they are situate under their chorion,
and even in its substance: they continually discharge, through
imperceptible orifices, a mucilaginous fluid, which lubricates
their free surface, and defends it from the impression of the
bodies with which it is in contact, at the same time that it
facilitates the passage of those substances.

35. These glands, which are very apparent in the bronchi, palate,
œsophagus, and intestines, where they take the name of the
anatomists who have particularly described them, are less obvious
in the bladder, the gall bladder, uterus, vesiculæ seminales,
&c. but the mucus which moistens the membranes unequivocally
demonstrates their existence. In fact, since this fluid is nearly
of the same nature on all the mucous surfaces, and, in those where
the glands are apparent, is evidently furnished by them, it must be
secreted in the same manner in those where they are less evident.
The identity of secreted fluids, certainly, supposes the identity
of the secreting organs. It should seem, that in situations
where these glands escape our observation, nature makes up for
their tenuity by increasing their number. In the lower animals,
particularly in the intestines, they form by their number a kind
of new layer, in addition to those we have described. The same may
be observed in the palate, velum, &c. in man.

36. There is therefore this great difference between mucous and
serous membranes; that the fluid which lubricates the former is
furnished by secretion, whilst that which moistens the latter is
produced by exhalation. We know but little of the composition
of mucous fluids, because in the natural state it is difficult
to collect them, and in the morbid state, where their quantity
increases, as for instance in catarrhs, their composition probably
undergoes some alteration: but their functions in the animal
economy are well ascertained.

37. The first of these functions is to defend the mucous membranes
from the impressions of the bodies with which they are in contact,
and which, as we have observed, are all heterogeneous to the
animal. Here, without doubt, we see the reason why the mucous
fluids are more abundant in the cavities where these bodies remain
for some time, as in the bladder, at the extremity of the rectum,
&c., than in those organs through which they merely pass, as in
the ureters, and in general in all the excretory ducts. Observe
again, why, when the impression of these bodies might be hurtful,
these fluids are poured out upon their surfaces in a much greater
quantity. The sound which is introduced into the urethra, and is
allowed to remain there; the instrument that is left in the vagina
to secure a polypus; that which, with a similar intention, remains
some time in the nasal fossæ; the canula, fixed in the lacrymal
sac, to remove the obstruction; and the tube that is introduced
into the œsophagus, when deglutition is interrupted, always
determine a more plentiful secretion upon the corresponding mucous
surface. This is one of the principal causes why it is so difficult
to retain elastic tubes in the trachea; the abundance of mucous
fluid, which is then separated, chokes up the apertures of the
instrument, and renders its frequent removal necessary, and may
even threaten the patient with suffocation, as Desault has himself
observed, although he has nevertheless many times succeeded with
that operation.

38. It therefore appears, that every acute excitement of mucous
surfaces determines, in the corresponding glands, a remarkable
augmentation of action. But how can this excitement, which does
not take place immediately upon the glands, have so great an
influence over them? For, as we have said, these glands are always
subjacent to the membrane, and are consequently separated by it
from the irritating bodies. It appears that the above fact belongs
to a general modification of the glandular sensibility, which is
susceptible of being put into action by every irritation upon the
extremities of the excretory ducts, which will be proved by the
following considerations: (1) The presence of food in the mouth
produces a more abundant flow of saliva. (2) The catheter fixed
in the bladder, and irritating the ureters, or their vicinity,
increases the flow of urine. (3) The introduction of a bougie, but
half way up the urethra, will often be sufficient to occasion the
bladder to contract with a power equal to force the urine through
the passage, and so to overcome an obstruction in the canal. (4)
The irritation of the glans, and of the extremity of the urethra,
sub coitu, determines the contraction of the vesiculæ seminales,
and augments the secretory action of the testes. (5) The action
of an irritating fluid on the tunica conjunctiva occasions an
abundant flow of tears. (6) In making experiments upon the state
of the abdominal viscera during digestion, and under the influence
of hunger, I have observed, that whilst the food is only in the
stomach there is very little flow of bile; but it increases
when the aliment passes into the duodenum, so that then there
is a considerable quantity in the intestines. During hunger the
gall bladder is distended, and but little bile flows into the
intestines. At the end of digestion, and even when that process
is half finished, the gall bladder contains but half of its full
quantity; yet it might be expected to empty itself more easily
during abstinence, for then the bile it contains is of a deep
green colour, very bitter, very acrid, and likely to irritate the
organ which encloses it. On the contrary, during, or immediately
after digestion, it is more clear, mild, and less irritating;
there must, therefore, be, during digestion, another stimulus: now
this stimulus is the aliment passing over the mouth of the ductus
communis choledochus[A].

39. Let us conclude, from these numerous considerations, that one
of the principal means that nature employs to augment the action
of the glands, and to excite that of their excretory ducts, is
irritation upon the extremities of these ducts. We must refer to
that cause the abundant secretion and excretion of mucous fluids
in the cases above stated. It is also to this susceptibility of
the mucous glands, to be excited by irritation at the extremities
of their excretory ducts, that we must attribute the artificial
catarrhs which are occasioned by the respiration of chlorine
gas; the flow of mucus which attends a polypus, any tumour in
the vagina, stone in the bladder, &c. The frequent occurrence of
leuchorrhea in women who use coition immoderately, the abundant
flow of mucus from the noses of those persons who take snuff, in
all these cases there is evidently an irritation of the mouths of
the mucous ducts.

40. The mucous membranes, by the continual secretion of which they
are the seat, perform a principal part in the animal economy.
They are to be regarded as one of the grand emunctories, by which
the residue of the nutriment constantly escapes from the body;
and consequently as one of the principal agents of that habitual
decomposition which carries away from living bodies the particles
which for some time formed part of the solids, but have at length
become heterogeneous to them.

41. Remark the fact, that none of the mucous fluids enter into
the circulation, but are thrown out externally; that of the
bladder, ureters, and urethra, with the urine; that of the vesiculæ
seminales and of the vassa defferentia with the semen; that of
the nostrils by the action of blowing the nose; that of the mouth
partly by evaporation, and partly by the anus with the excrements;
that of the bronchi by the pulmonary exhalation, which is effected
principally by the solution of this mucous fluid in the air of
respiration; those of the œsophagus, of the stomach, of the
intestines, of the gall bladder, &c., with the excrements of which
they frequently form, in the ordinary state, a part nearly equal to
the residue of the aliment; and they even compose almost the whole
of the matter voided in certain dysenteries and fevers, where the
quantity is evidently disproportionate to the food that has been
taken. Let us observe on this subject, that in the analysis of the
fluids, in contact with the membranes of which we speak, as the
urine, bile, gastric juice, &c., there are always some errors,
because it is very difficult, impossible even, to separate them
from the mucous fluids.

42. If we call to mind what has been said above, upon the extent
of the two general mucous surfaces, that they are equal and even
superior to the extent of the cutaneous organ; if we afterwards
contemplate these two grand surfaces, constantly throwing off the
mucous fluids, we shall see of what importance this evacuation
must be in the economy, and of what derangements its lesion may
become the source. It is doubtless to this law of nature, which
ordains that every mucous fluid shall be rejected externally, that
in the fœtus we must attribute the presence of the unctuous fluid,
of which the gall bladder is full, and of the meconium choking up
the intestines, &c., kinds of fluids which appear to be only a
collection of mucous juices, which, as they cannot be evacuated,
remain, until birth, upon the organs where they have been secreted.

43. It is not the mucous fluids only that are rejected externally;
almost all the fluids, separated from the mass of blood by the
means of secretion, have the same destiny: this is evident in
the most considerable part of the bile. It is very probable,
also, that the saliva, the pancreatic juice, and the tears, are
discharged with the fæces, and that it is their want of colour
alone that prevents them from being distinguished like the bile.
I do not know even if, in reflecting on a crowd of phenomena, one
would not be tempted to establish, as a general principle, that no
fluid, separated by secretion, returns into the circulation; that
this destination belongs only to fluids separated by exhalation,
as those of the serous cavities, of the articulations, of the
medullary organ, &c. that all the fluids are thus excremental or
recremental, and that there is no recremental excrement, as the
common division points out[B].

44. What is certain, at least, is, (1) that I have never been able
to effect the absorption of bile or saliva by the lymphatics.
When I have injected them into the cellular tissue of an animal
they have always produced inflammation and suppuration. (2) We
know that the urine, when infiltrated, does not become absorbed,
and that it strikes with death every part that it touches; whilst
the infiltrations of lymph, or of blood, are readily absorbed.
(3) There is an essential difference between the blood and the
secreted fluids as concerns their decomposition, whilst exhaled
fluids and serum, &c., are in that respect very similar.




SECTION V.

OF THE VASCULAR SYSTEM OF MUCOUS MEMBRANES.


45. The mucous membranes receive a great number of vessels: the
remarkable redness which distinguishes them would be sufficient
to prove it to us, if it could not be demonstrated by injections.
This redness is not everywhere uniform; it is less in the bladder,
large intestines, and frontal sinuses; very marked in the stomach,
small intestines, and vagina, &c. It is produced by a web of
very numerous vessels, whose supplying branches, after having
passed through the chorion, finish on its surface by an infinite
division, embracing the corps papillaire, and is covered only by
the epidermis.

46. It is the superficial position of these vessels that frequently
exposes them to hæmorrhages, as we remark principally in the nose,
and as is seen in hæmoptysis, hæmatemæsis, hæmaturia, in certain
dysenteries, where the blood escapes from the parieties of the
intestines, in uterine hæmorrhages, &c. so that those spontaneous
hæmorrhages, which are independent of any external violence applied
to the open vessels, appear to be special affections of the mucous
membranes; they are seldom observed but in these organs, and they
form at least one of the grand characteristics which distinguishes
them from all the other membranes.

47. It is also the superficial situation of the vascular system of
mucous membranes that renders their visible portions, as on the
lips, the glans, &c. serviceable in showing us the state of the
circulation. Thus, in various kinds of asphyxia, in submersion,
strangulation, &c., these parts present a remarkable lividity; the
effect of the difficulty that the venous blood finds in passing
through the lungs, and of its reflux towards the surfaces where the
venous system arises from that of the arteries.

48. I have already observed in the fœtus, and newly born infant,
that the vascular system is as apparent in the cutaneous organ
as in the mucous membranes; that the redness is there the same;
it is even in that part more marked in the earlier periods of
conception; but soon after birth all the redness of the skin seems
to concentrate itself upon the mucous membranes, which before,
being inactive, had no need of so considerable a circulation, but
which, becoming all at once the principal seat of the phenomena
of digestion, of the excretion of the bile, of the urine, of the
saliva, &c., demand a larger quantity of blood. The long continued
exposure of mucous membranes to the air frequently occasions them
to lose their characteristic redness, and they then assume the
colour of the skin (as M. Sabattier has well observed in treating
on prolapses of the uterus and vagina). By this circumstance some
have been deceived in believing such instances to be cases of
Hermaphrodism.

49. An important question in the history of the vascular system of
the mucous membranes presents itself, which is, does this system
admit more or less blood, according to its various circumstances?
As the organs within which this sort of membrane is spread are
nearly all of them susceptible of contraction and dilatation, as
is observable in the stomach, intestines, bladder, &c., it has
been believed, that during their dilatation the vessels, being
more spread out, received more blood, and that during their
contraction, on the contrary, being folded on themselves, and as
it were strangulated, they admitted but a small portion of this
fluid, which then flows back into the adjacent organs. M. Chaussier
has applied these principles to the stomach, the circulation of
which he has considered as being alternately the inverse of that
of the omentum, which receives, during the vacuity of that organ,
the blood which it, being in a state of contraction, cannot admit.
Since M. Lieutaud, an analogous use has been attributed to the
spleen. Observe what I have ascertained on this subject from the
inspection of animals opened during abstinence, and in the various
periods of digestion.

50. (1) Whilst the stomach is in a state of repletion its vessels
are more apparent on its exterior surface than during its vacuity;
its mucous surface at this time has no higher degree of redness,
but it has sometimes appeared to me to be less red than when the
viscus was empty. (2) The omentum, being less extended during
the plenitude of the stomach, presents nearly the same number of
apparent vessels, equal in length, but more folded upon themselves
than during the vacuity of that organ[C]. If they are then less
loaded with blood the difference is scarcely perceptible. I would
here observe, that great care is requisite in opening the animal,
or the blood will fall upon the omentum, and prevent us from
ascertaining its real state. (3) I am confident that there is no
such constant relation between the volume of the spleen and the
stomach in its different states of vacuity or plenitude; and if
that organ increases and diminishes under various circumstances,
it is not always in the inverse ratio of the state of the stomach.
Like Lieutaud, I at first made experiments on dogs, in order to
satisfy myself respecting the facts just stated; but the inequality
in the size and age of those which were brought to me leading
me to fear that I might not be able to compare their spleens
correctly, I repeated them on Guinea pigs, whose size and condition
corresponded, and examined, at the same time, some whilst the
stomach was empty, and others whilst it was full. I have almost
always found the volume of the spleen nearly equal, or at least the
difference has not been very perceptible. Nevertheless, in other
experiments I have seen the spleen, under various circumstances,
to show variations in its volume, but more particularly in weight;
and this was the same during digestion as after that process was
finished. From what has been said it appears, that if, whilst the
stomach is empty, there is a reflux of blood to the omentum and
spleen, it is less than has been commonly asserted. Moreover,
during this state of vacuity, the numerous folds of the mucous
membrane of this viscus leaving it, as we have before said, almost
as much extent of surface, and consequently of vessels, as during
its plenitude, the blood must circulate there nearly as freely as
when the viscus is in a contrary state; it has therefore no real
obstacles; the only impediment is in consequence of the tortuous
direction the vessels are then thrown into. Now this obstacle is
easily surmounted, since the vessels suffer no constriction or
diminution of calibre by the contraction of the stomach.

51. As respects the other hollow organs, it is difficult to examine
the circulation of their adjacent viscera during their plenitude
or vacuity; for their vessels are not superficial, as in the
omentum, or insulated, as in the spleen; therefore, to decide
this question concerning them, we can only observe the state of
the mucous membranes upon their internal surface. Now they have
always appeared to me as red during the contraction as during the
dilatation of the organs. Finally, I give this only as a fact,
without pretending to draw any inference from it opposed to the
common opinion. It is, in fact, possible, that though the quantity
of blood be always nearly the same, the rapidity of the circulation
may increase; and consequently, in a given time, more of this
fluid will be sent there during the plenitude of the viscera. This
appears to be necessary for the secretion of the mucous fluids,
which are then more abundant.




SECTION VI.

OF THE VARIATIONS IN THE ORGANIZATION OF MUCOUS MEMBRANES IN
DIFFERENT REGIONS.


52. The assemblage of the epidermis, corps papillaire, chorion,
glands, and vessels, constitutes in the mucous membranes their
intimate organization, which presents very considerable variations
in the different regions in which they are examined. I shall point
out only the principal of them; for in no different parts do these
membranes present the same appearance, and in order to describe all
their differences they should all be examined.

53. One of these variations is that which the aspect of mucous
membranes presents at their origin, when compared with their
appearance in the more remote parts of the organs. Compare, for
instance, the surface of the glans, the inner surface of the
lips, the orifice of the urethra, &c., with any portion of the
inner surfaces of the stomach, intestines, &c. In the first the
corps papillaire will be seen slightly marked, and offering no
villous character, the epidermis thick, very distinct, and easily
separated, the chorion very evident, the vessels rather less
superficial, the mucous glands numerous and very large, more
especially in the mouth; in the other characters almost opposite
will be observed; we should say, that the mucous membranes have
at their origin a structure of a middle kind between the skin and
their deeper portions.

54. Another variation of structure, not less striking, is that
which is met with in that portion of mucous surface which lines
the sinuses. Here it has more redness, and an extreme tenuity;
the three layers cannot be distinguished; and although there is a
considerable secretion of mucous fluids, there are no perceptible
mucous glands. Such are the characters of those portions of the
pituitary membrane, which are considered as adapted to augment the
sensation of smell, but which do not perform that function in the
manner generally understood. In fact, the instant when an odour
enters the nose, having the air for its vehicle, it cannot at once
pass into the sinuses, because the orifices by which these cavities
communicate with the nose are very small; but it enters gradually,
impregnates all the air which they contain, and not being able to
escape readily, for the same reason that rendered its entrance
difficult, the sensation is prolonged, which on the general
pituitary membrane is soon dissipated by the action of the fresh
air. Thus therefore the pituitary membrane is destined to receive
the impressions of odours, and its extensions into the cavities of
the sinuses to retain them.

55. With regard to the particular structure of that portion of
mucous membrane which lines the sinuses I remark, that it is
absolutely the same as of that which is spread over the surface
of the internal ear, with the exception of a still more delicate
tissue. All anatomists call this membrane the periosteum of the
bony covering of the internal ear. The following considerations
prove that it is not a fibrous membrane, analogous to that which
covers the bones, but a mucous layer, like that of the sinuses. (1)
It is evidently seen to be a continuation of the pituitary membrane
by the medium of the Eustachian tube. (2) It is found to be
habitually moist with a mucous fluid, which is discharged through
that tube, a property foreign to fibrous membranes, both of whose
surfaces are always attached to some parts of the animal structure.
(3) No fibre can be distinguished in it. (4) Its spongy appearance,
though whitish, its softness, the readiness with which it gives way
to the least agent directed against it, with a view to tear it,
form a character not to be found in any part of the periosteum.

56. I pass over the other variations of structure in mucous
membranes in their different regions; in all they have real
differences. I observe only, (1) That these variations distinguish
them from serous membranes, whose aspect is everywhere the same, as
may be seen by comparing the pericardium with the peritoneum, &c.
(2) The sensibility of mucous membranes varies in a very peculiar
manner in their different portions: thus an emetic irritates the
stomach, but not the conjunctiva; the pituitary membrane perceives
only odours; the mucous surface of the tongue flavours, &c. On the
contrary, the contact of all kinds of bodies with the naked serous
membranes produces phenomena exactly analogous.




SECTION VII.

OF THE VITAL POWERS OF THE MUCOUS MEMBRANES.


57. The sensibility of mucous membranes is one of the principal
characteristics that distinguishes them from other analogous
organs. This power, which belongs to organic bodies, is variable
in every part, prompt to develop itself in some parts, under
the influence of the least excitement, roused with difficulty
in others, present in every part, liable to proceed by means
of inflammation from the most obscure state to the last degree
of intensity--this power is here remarkable for features very
analogous to those which it presents in the cutaneous surface (to
which, as we have stated, the mucous surface has great traits of
resemblance) as respects its structure. It is to this analogy of
sensibility that we must refer a crowd of phenomena, which are
alternately exhibited in an inverse order upon both surfaces. I
shall now point out some of these phenomena in succession.

58. (1) When the temperature of the surrounding air deadens the
sensibility of the cutaneous organ, by contracting its tissue, the
sensibility of the mucous surface receives a remarkable increase
of energy. Observe why in winter, and in cold climates, where the
functions of the skin are singularly limited, all those of the
mucous membranes are in proportion augmented; thence arises a more
evident pulmonary exhalation, the internal secretions are more
abundant, digestion is more active and more ready to operate,
consequently the appetite is the more easily excited. (2) When,
on the contrary, the heat of the climate, or of the season, &c.
relaxes and opens the cutaneous surface, we should say, that the
mucous surface is in proportion constricted: during summer, in
the south, &c. there is a diminution in the internal secretions,
the urine for instance; a tardiness in the digestive phenomena
by a default in the actions of the stomach and intestines, and
the appetite is slow in returning. (3) The sudden suppression of
the functions of the cutaneous organ often determines a morbid
increase of action in those of the mucous membrane. Cold air, which
checks the perspiration, frequently produces colds and catarrhs,
affections which are marked by the sensibility and increased action
of the mucous glands. (4) In various affections of the mucous
membranes, baths, which relax and determine to the skin, produce
beneficial effects.

59. The foregoing considerations evidently establish the influence,
which the vital powers of the skin have over those of the mucous
membranes. Others, not less important, demonstrate the reciprocal
dependence in which the skin is found with the same membranes, as
respects their vital powers. (1) During digestion, when the mucous
fluids are poured out in abundance into the stomach and intestines,
when, consequently, the mucous membranes of the alimentary canal
are in high action, the fluid of insensible perspiration is
evidently diminished, according to the observation of Santorius:
it is very small in quantity three hours after a meal, so that
the action of the cutaneous organ is visibly less energetic. (2)
During sleep, when all the internal functions become more marked
and are in full action, at which time the sensibility of the mucous
membranes is consequently highly excited, the skin appears to be
seized by a manifest debility--a debility, which is evinced by
the cold which it experiences when the animal reposes at night
uncovered, and by its want of susceptibility of various impressions.

60. The sensibility of the mucous membranes, like that of the
cutaneous organ, is essentially submissive to the immense influence
of habit, which, tending incessantly to blunt the acuteness of the
sensations of which they are the seat, reduces the pain and the
pleasure that we receive through them equally to indifference,
which is, as some say, the middle state.

61. I say, in the first place, that habit reduces the painful
sensations, which take place on mucous membranes, to indifference.
The presence of the catheter, which is passed up the urethra
for the first time, is cruel the first day, painful the second,
inconvenient the third, scarcely felt the fourth; pessaries
introduced into the vagina, bougies into the rectum, tents in the
nasal fossæ, the canula in the nasal canal, produce, in different
degrees, the same phenomena. It is upon this remark that is founded
the possibility of introducing instruments into the trachea to
aid respiration, and into the œsophagus to afford artificial
deglutition. This law of habit may even transform a painful into a
pleasant impression; of this fact the use of snuff, tobacco, and
various kinds of food, furnish us with remarkable examples.

62. In the second place I observe, that habit produces indifference
to those sensations on the mucous membranes which were at first
agreeable. The perfumer placed in a fragrant atmosphere, and the
cook, whose palate is constantly affected by delicious flavours, do
not experience, in their professions, the exquisite pleasures that
they prepare for others. Habit may even change pleasant sensations
to painful ones, as in the preceding paragraph we saw it changed
painful to pleasing sensations. I observe, further, that this
remarkable influence of habit is exercised only over sensations
produced by simple contact, and not over those produced by real
lesion of the mucous membranes: thus it does not ameliorate the
pain produced by stone in the bladder, nor that which attends
polypus in the uterus.

63. It is to this power of habit over the vital energies of
the mucous membranes that we must, in part, refer the gradual
diminution of their functions which accompanies advancing age. All
is susceptibility in the infant: in old age all is dull. In the one
the very active sensibility of the alimentary, biliary, urinary,
and salivary mucous surfaces, is that which principally produces
that rapidity with which the digestive and secretory phenomena
succeed each other. In the other this sensibility, weakened by the
habit of contact, does not so closely connect the same phenomena.

64. Does not the following remarkable modification of the
sensibility of the mucous surfaces depend upon the same cause,
_viz._ that at their origin, as on the pituitary membrane, the
glans, the anus, &c., they give us the sensations of bodies with
which they are in contact, and that they do not produce this
sensation in the deeply seated organs which they line, as the
intestines, &c.? In the interior of these organs this contact is
always uniform; the bladder is in contact with the urine only,
the gall bladder with the bile, the stomach with the aliments
masticated and reduced to an homogeneous, pulpy paste, whatever
may be their diversity. This uniformity of sensation prevents
perception, because, in order to perceive, we must compare, and
here two terms of comparison are wanting. Thus the fœtus has no
sensation of the liquor amnii: the air is also very irritating at
first to the new-born infant, but at length it is not felt. On the
contrary, at the origins of mucous membranes exciting agents vary
every instant: the mind can, therefore, perceive their presence,
because it is able to establish relations between their various
modes of action. What I say is so true, that if in the interior of
the organs the mucous membranes be in contact with a foreign body
differing from that which is habitual to them, they transmit the
sensation of it to the mind; instruments introduced into bladder or
stomach are examples of it. Fresh air, which in very hot weather is
suddenly introduced into the trachea, causes an agreeable sensation
over the surface of the bronchi; but from habit we soon become
insensible to it, and the perception ceases.

65. It is very difficult to point out with precision the character
of the tonic powers of mucous membranes, because, being almost in
every part united to a muscular layer, we can hardly distinguish
what belongs to the tonicity of the one from what depends upon the
irritability of the other; or otherwise, if the mucous membranes
be isolated, as in the nostrils, yet their attachment renders the
phenomena of their tonic powers very obscure. Nevertheless, the
action of the excretory ducts on their respective fluids, that
of the gall bladder, and of the vesiculæ seminales, which are
destitute of muscular attachments, and the spasmodic contraction
of the urethra, which sometimes takes place when the sound is
introduced, leave no doubt of the energy of this tonic power,
doubtless similar in its various modifications to that which is
observed in the cutaneous organ.




SECTION VIII.

OF THE SYMPATHIES OF MUCOUS MEMBRANES.


66. I distribute the sympathies of mucous membranes, like those of
most of the other organs, into three general classes. In the first
class are ranked the sympathies in which irritation, on one part of
the mucous surface, produces a sensation in a distant part. A stone
in the bladder occasions pain at the end of glans; worms in the
intestines excite an itching at the nose. Whytt has seen a painful
affection induced over the whole side of the head by a foreign
body in the ear; an ulcer in the bladder produces a pain in the
superior parts of the thighs every time that the patient passes his
urine.

67. I refer to the second class those sympathies in which the
irritation of one point on mucous surfaces produces irritability
in a different structure; thus, too lively an impression on the
pituitary membrane occasions sneezing; the irritation of the
bronchi coughing; biliary concretions produce spasmodic vomiting;
stones in the bladder occasion retraction of the testicle towards
the ring. In all these cases there is contraction of the muscles
produced by the irritation of the mucous surface, distant from the
place in which that contraction occurs.

68. The last class of the sympathies of mucous membranes embraces
those in which the irritation of any part of their extension
determines elsewhere the exercise of their tonicity. Here we must
refer to what we have said upon glandular action being augmented
by the irritation of the extremities of the excretory ducts. Thus
it is evident, that the increase of the tonic power of the parotid
for the secretion of the saliva, and of its excretory duct in order
to transmit it, when the extremity of this duct is irritated by
food, sialogogue medicines, &c.,--it is evident, I say, that this
augmentation is a phenomenon purely sympathetic. We may designate
each of these three classes by the name of the vital power which
they bring into action, calling the first sympathy of sensibility;
the second, sympathy of irritability; and the third, sympathy of
tonicity.

69. This manner of classing the sympathies is entirely borrowed
from the state of the vital powers, of which they are but irregular
modifications, and only aberrations, still unknown in their
nature. Nevertheless it is subject to very great inconveniences:
yet it appears to me to be preferable to that of Whytt, who simply
follows the order of the regions; and even to that of Barthy, who,
more methodical, examines them successively in the organs connected
by systems, in those which are insulated, and in those situated in
symmetrical halves of the body.




SECTION IX.

OF THE FUNCTIONS OF MUCOUS MEMBRANES.


70. I have already examined many of the functions of mucous
membranes. I have considered them (1) As one of the grand
emunctories of the animal economy. (2) As performing the same
functions with respect to heterogeneous bodies, which may be within
our organs, as the skin does with regard to the bodies with which
it may be in contact. (3) As facilitating the passage of foreign
bodies by means of the mucous fluid by which they are lubricated.
It remains for me to examine three questions much agitated at
this time. (1) If the mucous membranes have any influence over the
redness of the blood. (2) If they exhale. (3) If the absorbents
arise from them; and if absorption consequently takes place there.

71. The remarkable redness of these membranes, the analogy of
respiration, during which the blood becomes changed in colour
through the mucous surface of the bronchi, the well-known
experiment of a bladder filled with blood and placed in oxygen gas,
by which this fluid becomes also changed in colour,--have led to
the belief, that the blood, being separated from the atmospheric
air merely by a very fine pellicle on certain mucous surfaces,
as the pituitary membrane, the palatine, the glans, &c., would
there also take a brighter red colour, either by parting with a
portion of carbonic acid gas, or by combining with the oxygen of
the atmosphere, and that these membranes thus fulfilled functions
accessory to those of the lungs. The experiments of Jurine upon the
cutaneous organ, experiments adopted by many celebrated physicians,
appear also to favour the reality of that conjecture.

72. Observe the experiment that I have tried, in order to ascertain
the validity of that fact. Through a wound in the abdomen I drew
out a portion of intestine, which I tied at one point. I then
returned it, keeping back a part, which I punctured, and introduced
into it sufficient atmospheric air to distend all that portion of
the bowel between the ligature and the orifice. I then confined the
air by another ligature, and reduced the whole. At the end of an
hour the animal was opened. I compared the blood of the mesenteric
veins, which arise from that portion of intestine distended by
air, with the blood of the other mesenteric veins arising from
the remainder of the canal: no difference of colour could be
observed: the internal surface of the inflated intestine did not
exhibit a brighter red. I expected to obtain a more marked effect
by repeating the same experiment on another animal with oxygen
gas, but I did not perceive any variation in the colour of the
blood. As on the mucous membranes, which are ordinarily in contact
with the air, this fluid is constantly renewed, and is agitated
by a perpetual movement, I tried to produce the same effect in
the intestines; for which purpose I made two openings into the
abdomen, through each of which I drew a portion of the intestinal
tube. I opened these two portions, adapting to one the tube of a
bladder filled with oxygen gas, and to the other that of an empty
bladder. I then pressed the full bladder so as to make the oxygen
gas pass into the empty one through the intermediate portion of
intestine which was in the abdomen, so that the warmth there might
encourage the circulation. The oxygen gas was in this manner sent
many times from one bladder to the other, making a current through
the intestine, which from its contraction was more difficult than
it at first appeared to be. The abdomen was then opened, but no
difference was found between the venous blood returning from that
portion of the intestine, and that which flowed from the other
parts of the canal. The superficial situation of the mesenteric
veins, which are covered by only a fine transparent lamina of
peritoneum, and their volume when the animal is not fat, render
these comparisons very easy to be made.

73. I think, that from what occurs in the intestines we cannot
infer what takes place in the pituitary and palatine membranes,
&c. because, although analogous, their organization may be
different. In these parts we cannot examine the venous blood
returning from them, as in the intestines: but, (1) If we consider,
that in animals, which have for some time respired oxygen gas, the
mucous membrane of the fauces does not exhibit any increase of
redness; (2) If we bear in mind, that the lividity of different
parts of this membrane, in those asphyxias which are produced by
carbonic acid gas, is not occasioned by the immediate contact of
this gas with the membranes, but by the reflux towards the surface,
of the venous blood which cannot pass through the heart, as occurs
in submersion, as demonstrated by Godwin, and as takes place in
all those cases in which the blood, previous to death, has found
difficulty in passing through the lungs; (3) If we remark lastly,
that in these circumstances the contact of the air, after death,
does not alter the lividity that the venous blood gives to the
mucous membranes, although the skin is then more permeable to
every kind of æriform fluid;--we shall see that we must at least
suspend our judgment, respecting the colouring of the blood through
mucous membranes, until farther observations shall have decided the
question.

74. Observe another experiment, which may throw more light still
upon the subject. I have distended the peritoneal cavity of
different Guinea pigs with carbonic acid gas, with hydrogen gas,
with oxygen gas, and with atmospheric air, to see if I could
obtain, through a serous membrane, what I had not been able to
effect through a mucous surface. In these experiments I have found
no difference in the colour of the blood of the abdominal system:
it was the same as in fresh animals of the same kind, that I
always used to compare with those on which the experiments were
made.

75. I believe, nevertheless, that I have observed many times, both
in frogs and in animals with warm and red blood, such as cats and
Guinea pigs, that the infiltration of oxygen gas into the cellular
tissue gives, after a certain time, a brighter colour to the blood
than this fluid presents in the artificial emphysemas which may
be produced by carbonic acid gas, hydrogen gas, or by atmospheric
air, in which circumstances the blood differs very little in colour
from its natural shade. But in other cases oxygen gas has had no
influence over the colour of the blood; so that, notwithstanding
the many experiments that have been made on this point, I cannot
state any general result. It appears, that the tonic powers of
the cellular tissue, and of the coats of the vessels which ramify
in it, receive a very varied influence from the contact of the
gases, and that, according to the nature of that influence, the
fibres contracting and becoming more or less firm render these
parts more or less permeable, both to the æriform fluids, which
have a tendency to escape from the blood to unite with that of the
emphysema, and to this last fluid, if it tends to combine with
the blood. This will doubtless explain the variations that I have
observed.

76. Do the mucous surfaces exhale? The analogy of the skin would
seem to lead to the belief of it; for it appears well proved, that
the perspiration is not a transudation by the inorganic pores of
the cutaneous surface, but a true transmission by vessels of a
particular nature, and continuous with the arterial system.

77. It appears, at first, that the pulmonary perspiration which
takes place on the surface of the bronchi, which has such
connection with that of the skin, which increases or diminishes
according to the decrease or augmentation of the other, and
of which the composition is apparently of the same nature--it
appears, I say, that the pulmonary perspiration is produced, at
least in part, by the system of exhalent vessels; and that if the
combination of the oxygen of the air concurs with the hydrogen of
the blood to produce it, during the act of respiration, it is but
in a very small quantity, and for that portion only which is purely
aqueous. It is necessary to observe further on this subject, that
the dissolution of the mucous fluid, which lubricates the bronchi,
in the air that is constantly inspired and expired, furnishes a
considerable portion of that vapour which rises from the lungs, and
which is insensible in summer, but very apparent in winter.

78. The intestinal juice, that Haller has particularly considered,
but which appears to be less in quantity than he had estimated,
the gastric juice, and that of the œsophagus, are very probably
disposed of by way of exhalation on their respective mucous
surfaces; but in general it is very difficult to distinguish with
precision, in these organs, what belongs to the exhalent system
from what is furnished by the system of mucous glands, which, as we
have said, are everywhere subjacent to them. Thus we constantly see
the mucous fluids of the œsophagus, stomach, and intestines, mix
themselves with the other fluids of these parts.

79. That mucous membranes absorb is evidently proved by the
absorption of the chyle upon the intestinal surfaces, of venereal
virus upon the glans and urethra, of variolous poison which is
sometimes rubbed upon the gums, of the serous portions of the
bile, of the urine, and of the semen, when they remain in their
respective reservoirs. When, from paralysis of the fleshy fibres
which terminate the rectum, the fæces accumulate at the extremity
of that intestine (a very common case in aged persons, and of which
Desault has cited many instances), these accumulations frequently
become hard, probably from the absorption of their juices, which
are obstructed there. We have many cases in which the urine has
been almost entirely absorbed by the mucous surface of the bladder,
when there has been absolute obstruction in the urethra. Whatever
may be the mode of this absorption, it appears that it is not
performed in a constant, uninterrupted manner, like that of the
serous membranes, in which the exhalent and absorbent systems are
in a continual alternate action; but that it occurs only under
certain circumstances, of which perhaps the greatest part are not
in the natural order of the functions. Finally, we have yet fewer
data respecting the mode of mucous absorption than on that of
cutaneous absorption: we confess it is very little understood, and
many even question its existence.




SECTION X.

REMARKS ON THE AFFECTIONS OF MUCOUS MEMBRANES.


80. It is not my design to examine the affections of mucous
membranes; I shall notice only some phenomena, which in these
affections I believe deserve a particular attention, and the
explanation of which I propose to physiological physicians.

81. Why do mucous membranes seldom contract adhesions from
inflammation, since that occurs so frequently in serous surfaces
under the same circumstances? Why does not the internal surface
of the inflamed stomach, intestines, or bladder, adhere in its
various portions like the pleura, tunica vaginalis, testis, &c.

82. Why, in inflammations of mucous membranes, is there an abundant
flow of that fluid which habitually moistens them, and which
constitutes the different kinds of catarrhs, whilst the source of
the fluid that exhales from serous membranes is generally dried up
in analogous cases?

83. Why do polypi, a kind of affection peculiar to mucous
membranes, seldom arise but at the origins of these membranes in
the vicinity of the skin, as in the nose, pharynx, vagina, &c., and
not in their more internal portions, as in the stomach, intestines,
&c.? Does this arise from the peculiarity of the texture that I
have shown mucous membranes to have in the vicinity of those places
where they arise from the skin, or must we attribute this fact to
the more numerous causes of irritation which act upon the origins
of these cavities?

84. Are not aphthæ an isolated inflammatory affection of the glands
of the mucous membranes, whilst catarrhs are characterized by a
general inflammation of all the parts of these membranes?


THE END.


CHARLES WOOD, Printer,

Poppin's Court, Fleet Street, London.




FOOTNOTES:

[A] The following questions have been much disputed: Is there a
cystic and an hepatic bile? Is the one of a different nature from
the other? Does their quantity increase or vary? &c. Contrary,
and even opposite, opinions have been supported by numerous
experiments made upon living animals, as Haller as well observed.
These experiments, though at first sight contradictory, in reality
are not so, as I have had the opportunity of convincing myself, by
repeating them in the different stages of digestion, and during
the abstinence of the animal, which previously had never been done
with precision. The following are what I have observed in dogs
that I have used in my experiments. (1) During abstinence, the
stomach and the small intestines being empty, yellowish clear bile
was found in the hepatic duct and ductus communis choledochus; the
surface of the duodenum and jejunum were stained by a bile which
had the same appearance; the gall bladder was very much distended
by a greenish bitter bile, which was deeper in colour and more in
quantity, according to the length of the abstinence. (2) During the
gastric digestion, which may be prolonged for a sufficient length
of time by giving the dog large pieces of meat, which he swallows
without chewing, appearances were similar. (3) At the commencement
of intestinal digestion, the bile in the hepatic duct was always
found yellowish; that of the ductus communis choledochus deeper in
colour; the gall bladder not so full, and its bile becoming already
more clear. (4) Towards the end of digestion, and immediately
after it, the bile of the hepatic duct, of the ductus communis
choledochus, that contained in the gall bladder, and that which was
spread over the duodenum, were exactly of the same colour as the
common hepatic bile, a clear yellow, having but little bitterness.
The gall bladder was but half full; it was not contracted, but
flaccid.

These observations, repeated a great number of times, evidently
prove, that such is the manner in which the bile flows during
abstinence and during digestion. (1) It appears that the liver is
continually separating from itself a sensible quantity of bile,
which increases during digestion. (2) That which is secreted during
abstinence is divided between the intestine, which is always found
coloured with it, and the gall bladder, which retains it without
transmitting any portion of it through the cystic duct, and where,
thus retained, it acquires a deeper colour and a character of
acrimony, necessary, without doubt, to the digestion which is soon
to follow. (3) When the food, having been digested by the stomach,
passes into the duodenum, then all the hepatic bile, which was
before divided, flows into the intestine, and even in greater
abundance; the gall bladder also pours that which it contains
upon the alimentary pulp, and with which it is then found quite
incorporated. (4) After the intestinal digestion the hepatic bile
diminishes, and begins to flow, part into the duodenum and part
into the gall bladder, where, being then examined, it is clear and
in small quantity, because it has not yet had time either to become
coloured, or to collect.

There is, therefore, this difference between the two kinds of bile,
that the hepatic flows in a continual manner into the intestine,
and the cystic, during the absence of digestion, flows back into
the gall bladder; and whilst that function is going on it passes
towards the duodenum; or rather it is always the same fluid, of
which one part preserves the character it has when it leaves the
liver, and the other part undergoes a change in the gall bladder.
The difference of colour in the cystic bile, according to the time
that it has remained in the gall bladder, is analogous to the
colour of the urine, which becomes deeper as it is retained longer
in its receptacle.

[B] The bile in the gall bladder, the urine in the bladder, and
the semen in the vesicula seminales, are certainly absorbed; but
it is not the fluid itself that re-enters the circulation, but
only its finest parts, some of its principles that we are not well
acquainted with, probably its aqueous or lymphatic portion. This
does not resemble the absorption in the pleura and other analogous
membranes, in which the fluid rejoins the blood in the same state
as it left it.

[C] This is a necessary consequence of the disposition of the
vascular system of the stomach. The arteria coronaria ventriculi
superior being situated transversely between the stomach and the
omentum, and furnishing branches to both, it is evident, that when
the stomach, by separating the duplicatures of the omentum, lodges
itself between them, and this in applying itself over the stomach
becomes shortened, the branches that it receives from that artery
cannot in the same manner apply themselves to it. To effect this
it would be necessary, that they should proceed from the one to
the other without the intermediate trunk that cuts them at right
angles; then the stomach, by distending itself, would separate them
in the same way that it does the omentum, and would lodge between
them, instead of pushing them before it with their common trunk,
and folding them upon themselves.




  TRANSCRIBER'S NOTE

  Italic text is denoted by _underscores_.

  Obvious typographical errors and punctuation errors have been
  corrected after careful comparison with other occurrences within
  the text and consultation of external sources.

  Except for those changes noted below, all misspellings in the text,
  and inconsistent or archaic usage, have been retained. For example,
  newly-born, newly born; circumvolutions; atmospherical.

  Pg v (TOC), page '101' replaced by '98'.
  Pg 54, 'the mach, small' replaced by 'the stomach, small'.
  Pg 57, 'membranes is spread' replaced by 'membrane is spread'.
  Pg 81, 'OF THE SYMPATHY' replaced by 'OF THE SYMPATHIES'.
  Pg 86, 'fine pelicle' replaced by 'fine pellicle'.
  Pg 90, 'those asphyxies' replaced by 'those asphyxias'.







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