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.