penetrating on the one hand by the urethra, goes as in man upon the
urinary organs; on the other hand, we see it enter the vagina, lining
it, the uterus and the fallopian tubes, and afterwards becoming
continuous with the peritoneum by the opening of these tubes. It is the
only example in the economy, of a communication established between the
mucous and serous surfaces.
This manner of describing the course of the mucous surfaces, by saying
that they are elongated, dip down, penetrate, &c. from one cavity to
another, is no doubt not conformable to the progress of nature, which
creates in each organ the membranes belonging to this organ, and does
not thus extend them by degrees; but our manner of understanding it
is better adapted to this language, the meaning of which the least
reflection will show.
In thus referring to two general membranes all the mucous surfaces,
I am not only supported by anatomical inspection, but pathological
observation has also furnished me with points of demarcation between
the two, and points of contact between the different portions
of membranes of which each is the assemblage. In the different
descriptions of catarrhal epidemics given by authors, we frequently
see one of these membranes affected in all parts, the other remaining
sound; it is especially not rare to observe a general affection of the
first, of that which extends from the mouth, the nose, the surface of
the eye, into the alimentary canal and the bronchial vessels. The last
epidemic observed at Paris, with which Pinal himself was affected,
was of this character; that of 1761, described by Razou, had it also;
that of 1752, described in the memoirs of the Society of Edinburgh was
remarkable for a similar phenomenon; now, we do not see at that time
a corresponding affection in the mucous membrane that is spread upon
the urinary organs and upon those of generation. There is then here,
1st, an analogy between the portions of the first, by the uniformity of
affection; 2d, a demarcation between the two by the health of the one
and the disease of the other.
We see also that the irritation of any one point of one of these
membranes, frequently produces a pain in another point of the same
membrane, which is not irritated. Thus a calculus in the bladder
occasions a pain at the end of the glans penis, the presence of worms
in the intestines causes an itching of the nose, &c. &c. Now, in
these phenomena purely sympathetic, it is very rare that the partial
irritation of one of these two membranes affects with pain one of
the parts of the other; there are however examples of it; such is
the singular relation that exists, in mucous hemorrhages, between
the membrane of the womb and that of the bronchia. If the blood
ceases accidentally to flow from one during menstruation, the other
frequently exhales it and thus as it were supplies its functions.
We ought then, from inspection and observation, to consider the mucous
surface, in general, as formed by two great membranes successively
spread upon many organs, having between them no communication except
by the skin, which serves them as an intermediate organ, and which,
continuing with both, contributes thus with them to form a general
membrane everywhere, continuous, covering the animal externally, and
extending within upon most of its essential parts. We can conceive
that there should exist important relations between the internal and
external portion of this single membrane; and that they do will be
proved by further researches.
II. _Adhering Surface of the Mucous Membranes._
Every mucous membrane exhibits two surfaces, one adhering to the
neighbouring organs, the other free, covered with villi, always
moistened with a mucous fluid. Each deserves particular attention.
The adhering surface corresponds almost everywhere with the muscles,
either of animal or organic life. The mouth, the pharynx, the whole
alimentary canal, the bladder, the vagina, the womb, a portion of the
urethra, &c. exhibit a muscular layer embracing on the outside their
mucous tunic which is within. This arrangement coincides perfectly, in
animals with a fleshy membrane, with that of the skin, which moreover
approximates very near, as we shall see, the structure of the mucous
membranes, and which, as we have seen, is everywhere continuous with
them. This arrangement of the mucous membranes occasions them to be
agitated by constant motions which favour wonderfully the secretion
that takes place in them, the excretion which succeeds it, and the
various other functions of which they are the seat. The insertion
of this muscular layer exterior to the mucous system, is made, as we
have seen, by this dense and compact texture which I have called the
sub-mucous. It is from this texture, more compact than the rest of the
cellular system, that the mucous surface derives its force. It is from
it that the organ which it lines receives its form; it is this which
supports and preserves this form; the following experiment proves it.
Take a portion of the intestine; remove from any part of it this layer,
as well as the serous and the muscular; then inflate it, after having
tied it below; the air produces in this place a hernia of the mucous
coat. Try afterwards another portion of intestine; deprive this, for a
small space, of its mucous membrane and of this also; inflation will
produce upon the serous and muscular tunics the same phenomenon that
it did in the preceding on the mucous; then it is to this sub-mucous
cellular layer that it owes the resistance with which it opposes
substances that it contains. The same may be said of the stomach, the
bladder, the œsophagus, &c.
III. _Free Surface of the Mucous Membranes._
The free surface of the mucous membranes, that which is continually
moistened by the fluid from which they borrow their name, exhibits
three species of wrinkles or folds.
1st. One inherent in the structure of all the laminæ of these
membranes, is constantly met with, whatever may be their state of
dilatation or contraction; such are those of the pylorus and the valve
of Bauhin. These folds are formed not only by the mucous membrane, but
also by the intermediate tunic of which we have spoken, which here has
a remarkable density and thickness, and gives them solidity. The fleshy
tunic enters even into their composition, and we see on the exterior,
upon the serous surface, a depression that indicates their presence.
2d. Other folds, only formed by the mucous surface, exist also always
in a state of vacuity or fulness, less evident however than this; they
are owing to the circumstance that the mucous surface is much more
extensive than those upon which it is applied, so that it is folded
that it may not run a longer course; such are the valvulæ conniventes
of the small intestines, the structure of which we see very well
by cutting longitudinally one of these intestines. The edge of the
section exhibits the fleshy layer and the serous surface in a straight
direction, whilst the mucous layer describes a line resembling a loose
thread.
3d. The last species of folds is as it were accidental, and is only
observed during the contraction of the organ which is lined by the
mucous surface that is the seat of it; such are those of the interior
of the stomach, the great intestines, &c. In the greatest number of
subjects brought to the dissecting rooms, these folds of which so
much has been said as it respects the stomach, cannot be perceived in
it, because the subject has died after a disease that has so altered
the vital forces, as to prevent all action of this viscus; so that
though it is frequently found empty, its fibres are not contracted.
In experiments upon living animals, on the contrary, these folds
become very evident, and may be demonstrated in this way; make a dog
eat or drink copiously, open him an instant after and cut the stomach
in the length of its great curvature; no fold is then apparent; but
soon the viscus contracts, its edges are turned over and the aliments
escape; the whole mucous surface is covered with an infinite number
of very prominent ridges, which have as it were the form of cerebral
circumvolutions. We obtain the same result by taking out the stomach
of an animal recently killed, distending it with air and opening it
afterwards, or by cutting it immediately in its state of vacuity and
drawing it in opposite directions by its edges; it stretches, its
ridges disappear, and if we cease to distend it, they form again
immediately in an evident manner. I would observe on the subject of the
inflation of the stomach, that by distending it with oxygen, we do not
produce by the contact of this gas, greater ridges and consequently
a stronger contraction, than by using for the same purpose carbonic
acid gas. This experiment furnishes a result very similar to what I
have observed in rendering animals emphysematous by different aeriform
fluids. It follows from all that we have said upon the folds of the
mucous membranes, that in the ordinary contraction of the hollow organs
which these membranes line they undergo but a very slight diminution
of surface, that they contract scarcely at all, but fold within, so
that by dissecting them on an organ in contraction we should have a
surface almost equal in extent to that which they exhibit during its
dilatation. This assertion, which is true as it respects the stomach,
the œsophagus and the great intestines, is not perhaps as entirely so
with regard to the bladder, the contraction of which makes the ridges
within less evident; but they are not sufficient to destroy the general
law. It is also nearly the same with the gall-bladder; yet here we
find another cause. The gall-bladder, alternately observed in hunger
and during digestion, contains double the bile in the first case
that it does in the second, as I have had occasion to see very often
indeed, in experiments made for this object or with other views. Now,
when the bladder is in part empty, it does not contract upon the bile
that remains, with the force of the stomach when it contains but few
aliments, or with the power of the bladder when it contains but little
urine. It is then flaccid; so that its being distended or not has but a
slight influence upon the folds of its mucous membrane.
Besides, in saying that the mucous membranes always exhibit, with some
slight difference, the same surface in the extension and contraction
of their respective organs, I intend to speak only of the ordinary
state of the functions, and not of those enormous dilatations of
which we often see the stomach, the bladder, and more rarely the
intestines become the seat. Then there is no doubt, a real extension
and contraction, which coincide in the membrane with those of the organ.
A remarkable observation which the free surface of the mucous membranes
exhibits, and which I have already pointed out, is, that this surface
is everywhere in contact with bodies heterogenous to that of the
animal, whether these bodies introduced from without to nourish it have
not yet been assimilated to its substance, as we see in the alimentary
canal and in the wind-pipe; or whether they come from within, as we
observe in all the excretory ducts of the glands, which all open into
cavities lined by the mucous membranes, and transmit without particles
which, after having contributed for some time to the composition of
the solids, become heterogeneous to them, and are separated from them
by the constant motion of decomposition which takes place in living
bodies. Hence we ought to regard the mucous membranes as limits, and
barriers, which, placed between our organs and the bodies that are
foreign to them, defend them from the mischievous impression of these
bodies, and serve consequently within, the same functions which the
skin performs without, with respect to the bodies which surround that
of the animal, and which tend incessantly to act upon it.
The organization of the mucous system and its vital properties are
accommodated to this habitual contact of substances heterogeneous to
the living economy. That which is a foreign body to the other systems,
the cellular, the muscular, &c. is not so to this. Solid substances,
the metals, stones, wood, &c. which introduced into our parts excite
in them inevitably suppuration and an antecedent inflammation by
their simple contact, pass with impunity over this, provided that
their angles and asperities do not tear it; they only augment a
little the secretion, as I shall say. We can swallow a ball of lead,
of wood, &c. and pass it by the anus without inconvenience. All the
irritating fluids without being caustic, that we inject into the great
intestines in enemas, or that we swallow, would produce abscesses,
&c. if they were forced into the cellular system, &c. Surgeons employ
the term foreign bodies in too general a manner; that which is so
for one system, is not for another. Foreign is, in this respect, a
term of comparison which we should employ only after a knowledge of
the peculiar sensibility of each system, and not after that of this
property described in a vague manner.
The mucous system not only bears without danger the presence of all
bodies that are introduced into the economy, but also when it goes out,
it can be exposed with impunity to the contact of external stimuli.
Observe what takes place in prolapsus of the womb in which the whole
membrane of the vagina sometimes becomes external, in those inversions
of the intestinal tubes that take place through preternatural ani, in
prolapsus of the rectum, &c.; then the mucous surfaces serve really as
integuments; now in these cases the surrounding bodies produce hardly
any more pain on them than upon the skin. On the contrary, the instant
a serous surface is laid bare, as for example in the operation of
hernia, in which the intestine is suffered to come out, on account of
an opening unfortunately made by the point of a bistoury, this surface
inevitably inflames. All the cellular, muscular, nervous, glandular
systems, &c. laid bare, exhibit the same phenomenon. There is no danger
in opening the bladder as it respects the contact of the air, whilst
there is much in permitting this fluid to penetrate into an articular
cavity, a tendinous groove, a serous sac, &c. We know how much in
the high operation for the stone, we fear to wound the peritoneum,
how uncertain are the results of empyema on account of the contact
of the air upon the pleura, &c. The dangers of the action of this
fluid upon these surfaces have been perhaps exaggerated, but they are
notwithstanding real.
If a fistula extends from the exterior of the abdomen into the
intestines, its whole course is lined with callous bodies; these defend
the cellular texture and the muscles through which the fistula passes.
On the contrary, nothing similar appears upon the intestinal mucous
surface, because its organization alone is sufficient to protect it.
The urinary, salivary and lacrymal fluids never escape externally by
artificial ducts formed in the neighbouring organs, without there are
similar callous bodies in the course of these ducts; on the contrary,
they pass with impunity over the mucous surfaces. Make in a limb a
long and straight opening with a pointed instrument, and fix in it for
a time a sound; a callous canal will be produced by it. Let a sound
on the contrary remain in the urethra, no alteration of texture will
result from it.
Let us conclude from these different considerations, that the mucous
system with the cutaneous alone, is organized so as to support the
contact of all external bodies, and not to be affected by their
presence, or at least experience only an increase of secretion, which
is in no ways dangerous. Thus these two systems form two boundaries,
the one internal and the other external, between which are placed the
organs foreign, by their mode of sensibility and by that of their
structure, to the external bodies. To these boundaries the excitement
of these bodies is limited; their influence does not go beyond. So
long as they do not pass these boundaries, the other organs do not
feel them. We might say that the acute sensibility which each of them
enjoys, is a kind of sentinel that nature has placed on the confines of
the organic domain of the mind, to inform it of whatever can injure it.
ARTICLE SECOND.
ORGANIZATION OF THE MUCOUS SYSTEM.
I. _Texture Peculiar to this Organization._
The mucous system presents two things to be considered in its peculiar
texture, viz. 1st, a layer more or less thick which constitutes
principally this texture, and which by analogy with the cutaneous
corion, may be called the mucous corion; 2d, many small elongations
which surmount it, and which are called villi or papillæ. As to the
epidermis which covers it, I shall treat of it with the cutaneous
epidermis. This texture has nothing similar to the substance that
colours the skin, and which is between the papillæ and epidermis. We
know in fact that negroes, as well as whites, have this texture of a
bright red, which it derives from its vessels.
_Mucous Corion._
This portion of the mucous texture, which is the most important, and
which constitutes the thickness, form, and even the nature of it, has
a soft and spongy appearance. We might say at first view that it was a
consistent pulp, with which the extremely dense cellular texture that
is subjacent to it had been covered. This softness is a character which
distinguishes it from the cutaneous corion, which moreover has by its
intimate nature but little resemblance to it.
The mucous corion is very various as to thickness; it differs in
this respect in each organ. That of the gums and the palate is the
thickest of all. Then come those of the nasal fossæ and the stomach,
then those of the small intestines and the gall-bladder, then those
of the large intestines, of the urinary bladder, the urethra and the
other excretories, until it begins at length to become so fine as to
appear transparent like a serous surface when it is removed with care.
Finally, the finest and most delicate is that of the sinuses of the
face and the interior of the ear; the arachnoides is often coarser.
I have called the texture within the ear mucous, though all anatomists
call the membrane of the cavities of this organ periosteum. In fact,
1st, we see it evidently continued with the pituitary membrane,
by means of the elongation of the Eustachian tube. 2d. We find it
constantly moistened by a mucous fluid which this canal serves to
convey out, a character foreign to the periosteum, which, like the
fibrous membranes, always adheres by both its surfaces. 3d. No fibre
can be distinguished in it. 4th. Its fungous appearance, though white
and soft, and the ease with which it is torn, are evident attributes
of the mucous membranes. Every thing proves that the membrane of the
tympanum, that of the meatus, &c. belong to the system of which we are
treating. Thus in catarrhs of the pituitary membrane, and of that of
the fauces, we most often find that the ear is affected; thus the ear
is, like the mucous surfaces, the seat of hemorrhage, thus polypi arise
in it, as in the nose and on the surface of the womb. We consider as a
sign of deposition of pus in the ear, every purulent discharge coming
from that cavity. But how can we conceive of a purulent collection in
a part in which there is hardly any cellular texture, in a part wholly
osseous? Besides the fibrous system, to which the periosteum of the
tympanum belongs, hardly ever suppurates, as we know. Every thing then
induces us to believe that these discharges are only the effect of a
catarrh of the ear, a catarrh which is sometimes acute and sometimes
chronic. I have moreover a recent and decisive fact upon this point;
the body of a man subject to these discharges during life exhibited
a remarkable thickness and redness of the membrane of the tympanum,
but without the least trace of erosion. The ear suppurates like the
urethra, the vagina, &c. it is not a new fluid which is formed by
suppuration; it is that which naturally comes from the meatus which
increases in quantity and comes through a preternatural opening of the
membrane of the tympanum.
Diseases make the thickness of all the mucous surfaces vary remarkably.
I have seen them many lines thick in the maxillary sinus, and nearly
half an inch in the bladder. In great extensions of the mucous
sacs, this thickness diminishes very much; it increases in their
contractions. The stomach especially exhibits this phenomenon in these
two opposite states.
The softness of the mucous corion is also very variable; in the nasal
fossæ, in the stomach and the intestines, it is really a kind of
organized velvet. The name of villous membrane is perfectly suited to
it. On the contrary, at the origins of the mucous system, as in the
mouth, upon the glans penis, at the entrance of the nose, it is a more
dense and compact texture, approximating nearer in its nature to the
cutaneous corion. I am persuaded that like this it might be tanned and
be useful in the arts if it were in larger pieces, whilst I doubt if
the action of tanning could produce an analogous phenomenon upon the
mucous texture of the deep-seated organs. The softness of this would
render it incapable of serving for external integuments. The least
cause would be in fact sufficient to break and tear it. Its structure
being different from that of the cutaneous corion is the reason that
the variolus pustules never appear on it, whilst we often see them on
the mucous surfaces near the openings of the skin, especially upon the
tongue, the palate and the internal surface of the cheeks.
Exposed to the action of dry air, so that it may come everywhere in
contact with it, it becomes dry and very thin, but preserves some
resistance. In bladders inflated and dried, in the stomach, the
intestines, &c. thus prepared, it is this texture which supports these
organs, and which prevents them from becoming flat, though we permit
the air to escape; it offers even a resistance, from which arises a
kind of crepitation when we wish to bend them in various directions. To
be convinced of this, it is only necessary to dry the mucous surface
separate from the serous and muscular that correspond with it; these
when dried remain pliable like the cellular texture, whilst the first
has a kind of rigidity.
In the organs in which the redness of the mucous texture is slight, as
in the bladder, the rectum, &c. it becomes transparent by drying. Where
it is very red as in the stomach, it takes a deep tinge, which becomes
even almost black if there had been an antecedent inflammation in it by
which much blood had been accumulated; hence it appears that this fluid
is the cause of the colour.
Thus dried the mucous surfaces are smooth; they lose their viscidity at
least in appearance; their folds are effaced by adhering to the surface
from which they arise; thus the valvulæ conniventes are marked in a
dried intestine, only by a red line, without any apparent prominence.
But if we macerate the intestines in this state, the folds form again
and become visible.
Exposed to a moist air, or left with other flesh that will not allow
it to become dry, the mucous corion putrefies with great ease; the
odour that it then sends out is very fetid. I think the reason why
the abdomen of dead bodies becomes putrid so soon is in part because
it contains substances already in putrefaction, and also because the
surfaces, in contact with these substances, and which by their vitality
resisted before their action, then readily yield to them. If these
substances were contiguous to aponeuroses, putrefaction would be much
less rapid. The mucous system when putrid takes a greyish colour; and
as the dense, subjacent cellular texture putrefies much less easily,
we can then remove from it by the least pressure, the mucous corion,
reduced to a putrid pulp, in which every trace of organization has
disappeared, and which forms a real pap.
During life, gangrene of the mucous texture takes place in general less
frequently than that of the cutaneous. The consequences of catarrh,
compared with those of erysipelas may convince us of this; there are
however cases in which death appears in this texture, whilst the
surrounding ones continue to live, as in gangrenous angina.