think that next to the brain it is altered quickest by the action of
water. It is then reduced to a reddish pulp very different from that
from putrefaction in the open air. When we put the whole stomach to
macerate, this pulp is detached, when the sub-mucous texture and the
serous membrane have as yet undergone but little alteration.
Ebullition at first extracts from the mucous texture a greenish scum,
very different from that which the muscular and cellular textures
give when boiled. This scum which mixed with the whole fluid in the
beginning of the boiling, disturbs it and renders it green at first,
afterwards rises upon the surface where it has small bubbles of air
mixed with its substance; it often even falls to the bottom of the
vessel by its weight. Sulphuric acid changes the colour of it to a dull
brown.
A short time before the water begins to boil, the mucous texture
crisps and acquires the horny hardness like the others, but in a
less degree however; hence why it is then wrinkled almost always in
different directions. In fact, the sub-mucous texture upon which it is
applied, contracting at that time much more than it, it must fold on
account of its length; thus during life, when the fleshy coat of the
stomach contracts, its mucous surface not contracting in proportion,
produces the numerous folds of which we have spoken. The action of a
concentrated acid crisping the sub-mucous texture more than the mucous
itself, produces an analogous phenomenon. After having been a long time
dried, the mucous texture, like however almost all those of the animal
economy, does not lose the faculty of acquiring the horny hardness when
it is plunged into boiling water; it exhibits this phenomenon, whether
we expose it to it dry, or whether we do it after having first softened
it in cold water. It is a means by which all the valvulæ conniventes
may be made suddenly to reappear, which had disappeared by drying, and
which form again the instant the intestine contracts. This experiment
is very curious to witness.
When the ebullition has been a long time continued, the mucous texture
turns gradually to a very deep grey, from the white which it had first
become. It is not softer than in the natural state, but it breaks
much quicker; the following experiment is a proof of it. If we draw
the mucous corion, boiled for some time with the subjacent cellular
texture, this last resists the most; so that it remains entire, whilst
the mucous corion is broken in many places. This never assumes the
gelatinous appearance of the cutaneous corion or the fibrous and
cartilaginous organs when boiled and of the others which yield much
gelatine. However by mixing a solution of tannin with the water in
which this system taken from an adult has been boiled, I have seen an
evident precipitate.
The action of the acids reduces to a pulp the mucous texture much
sooner than most of the others. During life, all the caustics act
much more rapidly upon it than upon the cutaneous, of which the
thick epidermis is an intermediate organ which checks their tendency
of combining with its corion. Thus the instant the nitric acid, a
substance which common people almost always choose for their poison, as
the practice at the Hôtel Dieu proves, thus the instant I say, that the
nitric acid is in contact with the alimentary canal, it disorganizes
it, it forms there a whitish eschar, which, when death does not take
place immediately, as most often happens, is slowly removed and
detached in the form of a membrane. We know that the lips gently rubbed
with weakened nitric acid, become the seat of a troublesome itching,
whilst that oftentimes though this acid may have acted upon the skin
sufficiently to make it yellow, it does not suffer from it.
The softness of the mucous corion makes me presume that it is easily
altered by the digestive juices, not that I confide in the experiments
of Hunter, who pretended that these juices could act upon the coat that
secretes them, but because in general I have observed that the textures
like it yield very easily to the action of water in maceration and are
also very easily digested. I have not however any experiment upon the
subject, and we know that in the animal economy analogy is not always a
faithful guide.
All the mucous surfaces, but especially that of the stomach and
intestines, have the property of curdling milk, as have many other
substances, especially the acids. Is it to this property that must
be attributed a phenomenon which is constant during life, viz. the
coagulation of milk that enters the stomach for digestion? or is
this phenomenon owing to the mixture of this fluid with those which
are secreted by the surface of this organ? I think that both these
causes contribute to it at the same time; both separate produce in
fact this phenomenon. Spallanzani has proved it as it respects the
gastric juices. Every body knows that the mucous membrane dried, and
consequently deprived of these juices, preserves the property of
coagulating milk. Spallanzani has convinced himself that the serous
and organic muscular systems of the stomach are destitute of it.
Are aphthæ an affection of the mucous corion? do they belong to
the papillæ? are they seated in the glands? are they a separate
inflammation of these glands, whilst catarrhs are characterized by a
general inflammation of a considerable extent of the mucous system? All
these questions deserve to be examined. Pinel has perceived the void
there is in morbid anatomy upon this point.
_Mucous Papillæ._
The peculiar kind of sensibility which the skin enjoys is attributed
principally, as we know, to what is called the papillary body, which
commonly is not easy to be demonstrated. The sensibility of the mucous
membranes, somewhat analogous to that of the skin, appears to me to
have the same kind of organization, which is perceived with infinitely
less ease. The papillæ of this system cannot be called in question at
its origin, where it dips into the cavities, in the commencement even
of these cavities, as upon the tongue, the palate, the internal part of
the alæ of the nose, upon the glans penis, in the fossa navicularis,
within the lips, &c. Inspection is sufficient to demonstrate them
there. But it is asked if the papillæ exist also in the deep-seated
parts of this system. Analogy indicates it, since the sensibility is
as great there as at their origin, though with varieties that we shall
point out; but inspection proves it in a manner not less certain. I
think that the villi with which we everywhere see them covered are
nothing but these papillæ.
Very different ideas have been entertained of the nature of these
villi; they have been considered in the stomach and the œsophagus as
destined to the exhalation of the gastric juice, in the intestines as
serving for the absorption of chyle, &c. But, 1st, it is difficult
to conceive how an organ everywhere nearly similar, can perform in
different parts functions so different; I say nearly similar, for we
shall see that these papillæ exhibit differences of length, size,
&c. without having any of texture or structure. 2d. What can be the
functions of the villi of the pituitary membrane, of the internal
coat of the urethra, the bladder, &c. if they have not relation to
the sensibility of these membranes? 3d. The microscopical experiments
of Leiberkuhn upon the vesicle of the intestinal villi have been
contradicted by those of Hunter, of Cruikshank and especially of
Hewson. I am certain that I have never seen any thing similar on the
surface of the small intestines, at the time of chylous absorption; and
yet it would appear that a thing of inspection could not vary. 4th. It
is true that these intestinal villi are everywhere accompanied by a
vascular net-work, which gives them a red colour very different from
the colour of the cutaneous papillæ; but the non-appearance of the
cutaneous net-work is owing to the pressure of the atmospheric air, and
especially to the contraction which it occasions in the small vessels.
Observe in fact the fœtus as it comes from the womb of its mother;
its skin is as red as the mucous membranes, and if its papillæ were a
little longer, it would resemble almost exactly the internal surface
of the intestines. Who does not know moreover, that the vascular
net-work surrounding the cutaneous papillæ, is rendered evident by fine
injections, so as to change their colour entirely?
That in the stomach this vascular net-work continuous with the
exhalants furnishes the gastric juice, and that in the intestines it
intermixes with the origin of the absorbents, so that these embrace
the villi, we cannot doubt after the experiments and observations of
anatomists who have recently engaged themselves in investigating the
lymphatic system. But this does not prevent the base of these villi
from being nervous, and them from performing upon the mucous membranes
the same functions that the papillæ do upon the cutaneous organ.
This manner of regarding them by explaining their existence generally
observed upon all the mucous surfaces, appears to me to be much more
conformable to the plan of nature, than to suppose them in each place
with different and often opposite functions.
Besides it is difficult to decide the question by ocular observation.
The delicacy of these elongations conceals their structure, even
from our microscopical instruments, agents from which anatomy and
physiology do not appear to me to have derived much assistance, because
when we see obscurely, each sees in his own way and according to
his own wishes. It is then the observation of vital properties that
should especially guide us; now, it is evident to judge by them, that
the villi have the nature I have attributed to them. The following
experiment served to demonstrate to me the influence of the papillary
body upon the cutaneous sensibility; it succeeds also upon the mucous
membranes. Remove the epidermis in any part and irritate the papillary
body with a sharp stilet; the animal is agitated, cries out and gives
marks of acute pain. Slide afterwards, through a small opening made in
the skin, a pointed stilet into the sub-cutaneous cellular texture, and
irritate the internal surface of the corion; the animal remains quiet
and makes no noise, unless some nervous filaments accidentally struck
make him suffer. Hence it follows very evidently, that it is upon the
external surface of the skin that its sensibility resides, that the
nerves pass through the corion without contributing to its texture, and
that their expansion takes place on the papillary body. It is precisely
so with the mucous surfaces. Observe that this circumstance coincides
very well with the functions of the two surfaces, which receive by
their free portion the action of external bodies, to which they are
foreign by their adhering portion.
The papillæ exhibit very great varieties. On the tongue, in the small
intestines, in the stomach and in the gall-bladder, they are remarkable
for their length. The œsophagus, the large intestines, the bladder,
all the excretory ducts have those that are less evident; these last
especially and the urethra in particular, are almost smooth in their
whole mucous surface. We can scarcely distinguish the papillæ in the
frontal, sphenoidal, maxillary sinuses, &c.
These small nervous eminences are sufficiently distinct and separate
upon the tongue. In the nasal fossæ, the stomach and the intestines,
they are so near together and at the same time so delicate, that the
membrane has at first view an uniform and smooth appearance, though
it is covered with these elongations. Each papilla is simple; no
bifurcation is ever observed at its extremity. All appear to have a
pyramidal form, if we can judge at least by those which are the most
evident.
Are they susceptible of a species of erection? It has been believed
with regard to those of the tongue, which become erect, it is said, to
perceive tastes, and with regard to those of the nose, which receive
odours more efficaciously in this state of erection, which is in the
sensitive phenomena on a small scale, what the erection of the corpora
cavernosa is on a large one. I do not believe that any exact experiment
can prove this fact. Moreover, it would be necessary then that the
intestinal, vesical papillæ, &c. should be in permanent erection, since
they are almost always in contact with foreign substances.
II. _Parts common to the Organization of the Mucous System._
Besides the blood vessels, the exhalants and the absorbents which
contribute to the structure of this system as to that of all the
others, it exhibits also a common organ, which is found almost always
separate elsewhere, but which is here especially designed for it. This
common organ is of a glandular nature; we shall now examine it.
_Of the Mucous Glands and of the Fluids which they secrete._
The mucous glands exist in all the system of this name. Situated
beneath the corion or even in its thickness, they pour out incessantly
through imperceptible openings a mucilaginous fluid which lubricates
its free surface, and which defends it from the impression of the
bodies with which it is in contact, and at the same time favours the
course of these bodies.
These glands are very apparent in the bronchia, palate, the œsophagus
and the intestines, in which they take the names of the anatomists who
have accurately described them, and where they make in many places
evident projections upon the mucous surface. They are less apparent in
the bladder, the womb, the gall-bladder, the vesiculæ seminales, &c.;
but the mucus that moistens them clearly demonstrates their existence.
In fact, since on the one hand this fluid is analogous on all the
mucous surfaces, and, on the other, in those in which the glands are
apparent, it is evidently furnished by them, it must be secreted in the
same way in those in which the glands are less evident. The identity
of the secreted fluids supposes in fact the identity of the secretory
organs. It appears that where these glands are hidden from our view,
nature compensates for their delicacy by their number. Besides, there
are animals in which, in the intestines especially, they form by their
vast number, a kind of new layer, in addition to those of which we
have spoken. In man this is remarkable in the palatine arch, in the
pillars of the velum, on the internal surface of the lips, the cheeks,
&c. &c. There is then this great difference between the mucous and the
serous membranes, that the fluid which lubricates one is furnished by
secretion, whilst that which moistens the others is from exhalation.
The size of the mucous glands varies; those of the velum of the palate,
those of the mouth, &c. are the largest; they become insensible in
the greatest number of mucous surfaces. I dissected two subjects that
died of a pulmonary catarrh, and in them the glands of the trachea and
bronchia, which are, as we know, very apparent, were not enlarged; the
membrane alone appeared to be affected. Besides, we do not yet know the
injuries of these glands, like those of the analogous organs, which
are more apparent from their size. They are in general of a rounded
form but with many varieties. No membrane appears to cover them. They
have, like the salivary glands and the pancreas, only the cellular
texture for an envelope. Their texture is more dense and compact than
these last glands; but little cellular texture is found in them; they
are soft, vascular, and appear when opened very much like the prostate
gland. I cannot say whether nerves penetrate them; analogy indicates
it, for all the principal glands receive them.
_Mucous Fluids._
We know but little of the composition of the mucous fluids, because
in the natural state, it is difficult to collect them, and in the
morbid, in which their quantity increases as in catarrhs for example,
this composition is probably changed. We know that in general they
are unsavoury, insipid, and but slightly soluble in water, in that
even which is raised to the highest temperature; they become putrid
with difficulty. In fact they remain a long time unchanged in the
nose, exposed to the contact of a moist air; in the intestines, they
serve, without danger to them, as an envelope for putrid substances,
&c.; taken from the body and subjected to different experiments, they
give results conformable to these facts. All the acids act upon them
and colour them differently; exposed to a dry air, they thicken by
evaporation, and are often even reduced to small shining laminæ. The
nasal mucus especially exhibits this phenomenon. Fourcroy has given
in detail the analysis of this mucus; he has also given that of the
tracheal mucus. But we must not apply rigorously to the analogous
fluids our knowledge of the composition of these. It is sufficient
in fact to examine a certain number of these fluids, to be convinced
that they are not the same in any two places, that more or less thick,
more or less uniform, different in their colour, their odour even, &c.
they vary in the principles that constitute them, as the membranes
which furnish them vary in their structure, in the number and size
of their glands, in the thickness of their corion, the form of their
papillæ, the state of their vascular and nervous systems, &c. I am far
from being certain that the gastric juice is a mucous juice; it is
even probable that exhalation furnishes it, the glands of the stomach
throwing out a different fluid by the way of secretion. But this
assertion is not accurately demonstrated, and perhaps hereafter it will
be proved that this juice, so different from the other mucous juices,
is however one of them, and that its properties are distinct only
because the structure of the mucous surface of the stomach is not the
same as that of the other analogous surfaces.
The functions of the mucous fluids in the animal economy are not
ambiguous. The first of these functions is to defend the mucous
membranes from the impression of the bodies with which they are in
contact, and all which, as we have observed, are heterogeneous to that
of the animal. These fluids form upon their respective surfaces a
layer which supplies, to a certain extent, by its extreme tenuity, the
absence of their epidermis. Thus where this membrane is very apparent,
as upon the lips, the glans penis, at the entrance of the nose and in
general at all the origins of the mucous system, these fluids are not
very abundant. The skin has only an oily layer, infinitely less evident
than the mucous of which we are treating, because its epidermis is very
distinct.
This use of the mucous fluids explains why they are more abundant
where heterogeneous bodies remain some time, as in the bladder, at the
extremity of the rectum, &c. than where these bodies are only to pass,
as in the ureters, and the excretory ducts generally.
Hence why when the impression of a body would be injurious, these
fluids are poured out in greater quantity upon their surfaces. The
sound which enters the urethra and remains in it, the instrument that
is left in the vagina to compress a polypus, that which remains some
time with the same view in the nasal fossæ, the canal fixed in the
lachrymal sac to remove the obstruction, that which is introduced into
the œsophagus to assist interrupted deglutition, always produce, upon
the portions of the mucous surface that corresponds to them, a more
abundant secretion of the fluid which is constantly poured out, a true
catarrh. This is one of the principal reasons that renders it difficult
to keep elastic sounds in the wind-pipe. The abundance of the mucus
that is then secreted, by closing the openings in the instrument,
renders frequent introductions necessary, and can even threaten the
patient with suffocation, as Desault himself has observed, though
however he obtained great advantage from this means, as I have shown
in his surgical works. I ought even to say, that since the publication
of the Treatise on the Membranes, I attempted to fix a sound in the
air tube of a dog, and that the animal died at the end of some time,
having the bronchia filled with a frothy fluid which appeared to have
suffocated him.
It appears then that every considerable excitement of the mucous
surfaces produces a remarkable increase of action. But how can this
excitement, which does not take place immediately upon the gland,
have so great an influence upon it? for, as we have said, these
glands are always under the membrane, and consequently separated
by it from the irritating bodies. It appears that it is owing to a
general modification of the glandular sensibility, which is capable of
being brought into action by any irritation upon the extremity of the
excretory ducts, as I shall prove in the glandular system.
It is to the susceptibility that the mucous glands have of feeling the
irritation made at the extremity of their ducts, that must be referred
the artificial catarrhs with which Vauquelin has been affected by
respiring the vapours of the oxy-muriatic acid, the mucous discharge
that attends the presence of a polypus, of any tumour in the vagina,
of a stone in the bladder, &c. the frequency of fluor albus in women
who are immoderate in the use of sexual intercourse, the more abundant
discharge of the mucus from the nostrils of those who take snuff, &c.
In all these cases, there is evidently excitement at the extremity of
the mucous ducts. I refer also to this excitement the mucous discharge
that takes place, from stimulating the end of the nipple of a woman who
does not give suck, the copious secretions which the presence of an
irritating body produces in the intestines, secretions which especially
furnish the matter of diarrhœas, the gastric derangements which succeed
an indigestion that has allowed to remain on the mucous surface of the
stomach substances not digested and consequently irritating; these
derangements are in fact real catarrhs of the membrane of the stomach,
catarrhs which most often are not connected with bilious turgescence.
I could add many other examples of the mucous secretions increased by
an irritation upon the surface of the membranes, at the extremity of
the excretory ducts; these will be sufficient to give an idea of the
others.
All these excitements produce a kind of inflammation, the peculiarity
of which is to contract at first for some time the glandular ducts, and
arrest the secretion, which they afterwards excite in great quantity.
When the mucous fluids have flowed abundantly for some time, they
gradually diminish though the cause continues; thus less mucus is
discharged from the urethra in proportion after the sound has remained
in it a month, than when first introduced; but almost always as long as
the cause continues, the mucous discharge is greater than in a natural
state.