the mucous lines the interior; such are the stomach, the intestines,
the bladder, the lungs, &c. We see it around all those that are
essential to life, as around the brain, the heart, all the gastric
viscera, the testicles, the bladder, &c. It does not form, like the
mucous system, a surface everywhere continuous upon the numerous
organs on which it is spread. But it is always found insulated in its
different divisions which never have any communication. The number of
these divisions is somewhat considerable. By considering in one view
all the different serous surfaces, we see that as a whole they exceed
the mucous surfaces viewed also in a general manner. One consideration
is sufficient to convince us of it. The mucous and serous surfaces
accompany each other in a very great number of parts, as in the
stomach, the intestines, the lungs, the bladder, the gall-bladder, &c.
so as to exhibit in them nearly the same extent. But on the one hand,
the mucous surfaces extend where the serous are not met with, as in the
nasal fossæ, the œsophagus, the mouth, &c. &c.; and on the other, there
is a very great number of serous surfaces existing separately from the
mucous, as the pericardium, the arachnoides, &c. Now if we compare
the extent of the separate serous surfaces, with that of the separate
mucous surfaces, we shall see that the first is much greater than the
other.
These considerations, apparently minute, deserve however particular
attention, on account of the relation of functions existing between
these two surfaces taken as a whole, a relation which is especially
connected with the exhalation of the albuminous fluids produced by one,
and with the secretion of the mucous fluids, of which the other is
the seat. Besides, in examining the extent of each serous membrane in
particular, we see great varieties from the peritoneum which has the
greatest surface, to the tunica vaginalis which has the least.
The serous surface taken as a whole, compared with the cutaneous
surface, is also evidently superior to it in extent; so that in this
respect, the quantity of albuminous fluids constantly exhaled within,
appears to be much more considerable than that of the fluid which is
incessantly thrown off by insensible transpiration; I say in this
respect, for different circumstances, by increasing the action of the
cutaneous organ, can re-establish the equilibrium in the exhalation
of these two fluids, one of which re-enters by absorption into the
circulation, and the other is wholly excrementitious. I do not know
even if the pulmonary and cutaneous exhalations united are not less
than those which take place upon the serous surfaces.
Every serous membrane represents a sac without an opening, spread upon
the respective organs that it embraces, and which are sometimes very
numerous, as in the case of the peritoneum, sometimes single, as in the
case of the pericardium, covering these organs so that they are not
contained in its cavity, and so that if it was possible to dissect them
from their surface, we should have this cavity whole. This sac has in
this respect the same arrangement as those night caps, which are folded
within themselves; a trifling comparison, but which gives an accurate
idea of this sort of membranes.
From this general arrangement, it is easy to understand that the
serous membranes are never opened to permit the vessels and nerves to
penetrate the respective organs to which they go or from which they
come off, but that they always wind round them and accompany them
to the organ, and thus form for them a sheath which prevents them
from being contained in their cavities; this removes the danger of
infiltration of serum which lubricates them, an infiltration which
would take place through the neighbouring cellular texture, especially
if they were dropsical; if, as in the fibrous membranes, they were
pierced with foramina for the passage of these vessels and nerves.
This arrangement, exclusively remarkable in the membranes of which we
are treating, and in the synovial ones, is evident at the entrance
of the vessels of the lungs, the spleen, the intestines, the stomach,
the testicles, &c. We see it very well in the arachnoides, a membrane
essentially serous, as I have demonstrated elsewhere.
From the general idea that we have given of these membranes, it is
also easy to understand how almost all are composed of two distinct
parts, though continuous, and embracing, the one the internal surface
of the cavity where they are found, the other the organs of this
cavity; thus there is a costal and pulmonary pleura, a cranial and
cerebral arachnoides, one portion of peritoneum spread upon the gastric
organs, and another upon the abdominal parietes, a free portion of the
pericardium, and one adhering to the heart. The same arrangement exists
in the testicles, &c.
Though the serous membranes may be separate, yet there sometimes
exists communications between them; that for example of the cavity of
the omentum with that of the peritoneum, that of the cavity of the
arachnoides with the cavity of the membrane which lines the ventricles
by the canal that I have discovered, and the external orifice of which
is seen below and at the posterior part of the corpus callosum; whilst
the internal one is seen above the pineal gland, between the two rows
of small round bodies which are usually found in this place.
There is but one example of continuity between the serous and mucous
membranes, that which exists, by means of the Fallopian tube, between
the peritoneum and the uterine surface. How does the respective nature
of the two membranes change here?
_Free Surface of the Serous Membranes._
Every serous membrane has one of its two surfaces free, everywhere
contiguous to itself, and the other adhering to the neighbouring
organs. The first is remarkable for its polish, which especially
distinguishes this system and the following, from all the other
membranes. All the organs which exhibit this arrangement owe it to the
covering they borrow from it. The liver ceases to be smooth and shining
at its diaphragmatic edge where the peritoneum abandons it. There is
in this respect a great difference in the appearance of the anterior
and posterior face of the cæcum. The bladder is rough wherever the
peritoneal covering is wanting. The cartilages of the ribs have not the
polish of those of the articulations which the synovial membrane covers.
Does this remarkable attribute of the serous membranes depend on the
compression exerted upon them? Their situation in places where they
are exposed to continual friction, would seem to make it probable.
Bordeu thought so, when he said that all the parts of the abdomen
are originally covered with cellular texture, which by pressure is
afterwards changed into membranes; so that the peritoneum is formed
partially upon each gastric organ, and its different parts give birth,
by uniting, to the general membrane. This explanation of the formation
of the peritoneum is applicable, according to him, to the pleura,
the pericardium, and all the analogous membranes. But if this is the
progress of nature, 1st, why, whatever be the period at which we
examine the fœtus, do we find the peritoneum and the serous membranes
as much developed in proportion, as their corresponding organs? 2d.
How are the numerous folds of these membranes formed, such as the
mesentery, the omentum, &c.? 3d. Why are there parts where they do not
exist though they are exposed to as great friction as that of the parts
where they are found? Why, for example, are the sides of the bladder
destitute of it, whilst it covers its superior part? 4th. Why does it
not also form serous surfaces around the great vessels of the arm, the
thigh, &c. which impart to the neighbouring organs an evident motion?
5th. Why does not the thickness of the serous membranes increase
where the motion is strongest and diminish where it is weakest? Why
for example does the thickness of the tunica vaginalis equal that of
the pericardium? 6th. How can friction internally produce an organized
body, whilst externally it constantly disorganizes the epidermis? 7th.
How can we associate the vascular lymphatic texture of the serous
membranes with the pressure that produces them? The impossibility of
resolving these numerous questions proves, that it is not to mechanical
pressure that must be attributed the formation of the serous membranes
and the polish of their surface; that their mode of origin is the same
as that of the other organs; that they commence and are developed with
them; that this polish is an evident result of their organization, as
the mucous papillæ depend upon the texture of the surfaces to which
they belong. What would be said of a system in which these papillæ
should be attributed to the pressure of the aliments upon the stomach,
of the urine on the bladder, the air on the pituitary membrane, &c.?
The free surface of the serous membranes separates entirely from the
neighbouring organs those upon which these membranes are spread; so
that they are to these organs real boundaries, barriers, if I may use
the term, or integuments, if it should be preferred, very different
however from those which are external. Observe in fact that all the
principal viscera, the heart, the lungs, the brain, the gastric
viscera, the testicles, &c. limited by their serous covering, suspended
in the middle of the sac that it forms, only communicate with the
adjacent parts where their vessels enter; everywhere else there is
contiguity and not continuity.
This insulation of position coincides very well with the insulation of
vitality which is remarked in all the organs, and especially in those
that we have just noticed. Each has its peculiar life, which is the
result of a particular modification of its vital forces, a modification
which necessarily establishes one in the circulation, nutrition and
temperature. No part feels, is moved and nourished like another, unless
it belongs to the same system. Each organ executes on a small scale the
phenomena which take place on a large one in the economy; each takes
from the circulation the aliment that is proper for it, digests it,
throws back into the mass of blood, the portion which is heterogeneous
to it, and appropriates to itself that which can nourish it; it is
digestion in miniature. No doubt the ancients wished to give an idea of
this truth which has been so well explained by Bordeu, when they said
that the womb was a living animal within another. A very important use
then of the serous membranes is to contribute, by rendering independent
the position of their respective organs, to the independence of the
vital forces, life and functions of these organs.
Let us not forget to consider under the same point of view, the moist
atmosphere with which they are constantly surrounded, an atmosphere
analogous to that which the cellular texture forms for various other
organs. In this atmosphere all the morbific emanations of the organ go
and are lost, if we may so say, without these emanations injuring the
other organs. We have seen that this atmosphere in the cellular system
is sometimes the seat of phenomena wholly different, and serves to
transmit diseases from one organ to another. Now the serous membranes
are a barrier much less easily surmounted, because they have not
filaments which go from one organ to another, there is only contiguity
as I have said, with the organs that they surround. We very rarely see
in the abdomen a disease of the liver communicated to the intestines,
one of the spleen passing to the stomach, &c.
The smoothness of the free surface of the serous system greatly
facilitates the motions of the organs which it covers. We have already
observed that nature employs two principal means for this object, viz.
the membranes and the cellular texture. By distributing externally
the second of these means, it has designed the first especially for
internal motions. The smoothness and moisture of the serous surfaces
are singularly favourable for them. These internal motions are usually
regarded only in an insulated manner, as relating to the functions of
the organ that executes them, as in relation to the circulation for
the heart, respiration for the lungs, digestion for the stomach, &c.
But they should also be considered in a general manner; they should be
regarded as carrying through the whole machine a continual excitement
which supports and animates the forces and the action of all the organs
of the head, the chest and the abdomen, which receive less sensibly
than the organs of the extremities, the influence of external motions.
It is these internal motions that excite, sustain, and develop within,
the nutritive phenomena, as the motions of the thigh, the arm, &c.
without, favour the nutrition of the muscles which are found there;
this is seen very evidently in bakers and other mechanics who exert
more particularly this or that part. It is thus that the serous
membranes contribute indirectly to the nutrition and growth of their
respective viscera; but they never have a direct influence upon this
nutrition, because their organization and life are different from the
life and organization of these viscera.
The free surface of the serous system differs essentially from that of
the mucous, in this, that it contracts frequent adhesions. The pleura
is of all the serous organs, that in which these adhesions are the most
evident. We find almost as many dead bodies in which they exist, as we
do those in which they do not. Next to the pleura is the peritoneum,
then the pericardium, then the tunica vaginalis, then the arachnoides,
which is that of all the serous surfaces in which adhesions are the
least frequent, though I have observed them in it. These adhesions
exhibit many varieties which can be studied best on the pleura, which
are as follows.
1st. Sometimes the costal and pulmonary portion are so identified at
many points or in every part, that they make but a single membrane, and
are united as closely as the two edges of the lip in a hare-lip that
has been operated upon with success. 2d. At other times the adhesion
is so slight, that the least effort is sufficient to destroy it. I
have many times noticed this fact in the pericardium. I saw it once in
the tunica vaginalis of a man who had been operated upon for hydrocele
by means of injection, at the time I was surgeon for operations at
the Hôtel Dieu. Separated then from each other, the two surfaces were
uneven; they lost their polish. 3d. Frequently between the costal
and pulmonary portion of the pleura, between the surfaces of the
peritoneum, &c. there are several elongations of various lengths, which
form a kind of loose bridles, traversing the serous cavity, having the
same organization and polish as the membrane of which they appear a
kind of fold, containing in their interior a species of small canal,
because they are formed by two layers united together, resembling
very much the elongation of the synovial membrane of the knee, which
goes from the posterior part of the patella to the space between the
condyles of the femur, having also an appearance analogous to the
different natural folds of the peritoneum. We can hardly conceive that
these filaments so regularly organized can result from inflammation. I
am inclined to believe that they are owing to an original conformation.
4th. Frequently between the two portions of the pleura, there are seen
many other elongations wholly different, which are not smooth, and do
not form canals, but which appear to be flocculent and really analogous
to the cellular layers; so that where they exist it may be said, that
the membrane is entirely changed into this texture, which is besides,
as we shall see, the essential base of its organization. 5th. I do
not speak of the adhesions produced by false membranes, by albuminous
flakes, intermediate to the two portions of a serous surface, &c. These
adhesions are to a certain point foreign to these surfaces.
II. _Adherent Surface of the Serous System._
The external surface of the serous membranes adheres almost everywhere
to the neighbouring organs; it is rare in fact to see these membranes
detached on both sides. The arachnoides at the basis of the cranium,
and some other examples are exceptions. This adhesion of the serous
membranes to their respective organs, is wholly different from that
of the fibrous membranes. In this last, the passage of the vessels so
unites the two parts, that their organization, seems to be common,
and when one is removed, the other almost always dies, as is seen in
the periosteum in relation to the bones, &c. On the contrary, every
serous membrane is almost foreign to the organ it surrounds; their
organization is different. The following are proofs of it;
1st. We very often see these membranes abandon and cover again
successively their respective organs; thus the broad ligaments, at a
great distance from the womb in the ordinary state, are to it like a
serous membrane during pregnancy. An intestine when distended borrows
from the mesentery a covering that quits it when it contracts. The
omentum is by turns, as Chaussier has well observed, a loose membrane
in the abdomen and a covering of the stomach. The peritoneal envelope
of the bladder often leaves it almost entirely. Has not the hernial sac
of those enormous tumours of gastric viscera originally served to line
the parietes of the abdomen? Now it is evident, since the different
organs can exist separate from their serous membranes, that there is
no connexion between their organization. 2d. It is always a loose
texture, easily stretched in every direction, that serves as a means of
union, and never a sanguineous vascular system, as in most of the other
adhesions. 3d. The affection of an organ is not a necessary consequence
of that of its serous membrane, and reciprocally the organ is often
affected and the membrane does not become diseased. For example, in the
operation for hydrocele, the testicle remains almost always sound in
the midst of the inflammation of its tunica vaginalis. The inflammation
of the mucous membrane of the intestines is not a consequence of that
of their peritoneal covering; and reciprocally in the various acute
catarrhal affections of the organs with a mucous membrane within and
a serous one without, this last is never found inflamed. In a word,
the affections of the mucous membranes are everywhere very distinct
from those of the serous, though most commonly both contribute to the
formation of the same organ. It is evident that a line of demarcation
so great in the affections supposes one of course in the organization.
The life of the serous membranes then is entirely distinct from that of
their corresponding organs.
Yet there are cases where these membranes do not present this loose
adhesion, and where they become so united to the organs which they
line, that frequently the most delicate scalpel cannot separate them.
Observe the tunica vaginalis on the albuginea, the arachnoides on the
dura-mater, and other membranes which form what I have called the
sero-fibrous, &c.; such is the connexion of these different surfaces,
that many have been mistaken to the present time for a single membrane.
There is however no more identity in the organization, than where the
serous membranes are more loosely attached to their respective organs,
as is seen in the peritoneum, the pleura, &c. Diseases sometimes
make this difference very evident. I have seen the arachnoides in a
subject that had been affected with a chronic inflammation, evidently
thickened on the internal surface of the dura-mater, without this
having experienced the slightest alteration; it was detached without
difficulty and torn with great ease.
III. _Serous Fluids._
Every serous membrane is moistened on its internal surface by a fluid
almost the same as the serum of the blood. The exhaling orifices
constantly pour it out and it is constantly taken up by the absorbents.
Its quantity varies. A mere dew in the natural state, it is exhaled
in vapour when the serous surfaces are laid bare and allow the air to
dissolve it. It is in general more abundant in dead bodies than in
the living, because on the one hand the transudation which the tonic
forces prevent, then easily takes place from the destruction of these
forces, and supplies the place of the vital exhalation, by transmitting
mechanically by their weight, the fluids of the surrounding organs to
the different serous cavities, and because on the other hand, this
destruction of the tonic forces prevents every kind of absorption;
hence the stagnation and accumulation of this fluid. We know to what an
extent this increases in various dropsies, especially in that of the
abdomen.
Does this quantity vary according to the different states of the
organs which the serous membranes cover? It has been long said, that
the synovia is exhaled in greater abundance in the motion of the
articulations, than in their state of rest. I have no data on this
point founded upon experiment; but I am certain that I have many times
observed in living animals, that the exhalation of the serous surface
of the abdomen does not increase during digestion, or at least if it is
greater, absorption becomes more active, and thus the surface of the
peritoneum is not more moist than at another time. I have opened the
thorax of many small guinea-pigs, after having first made them run
a long time in the chamber in order to accelerate their respiration,
and I have not observed greater moisture on the pleura. Yet it cannot
be doubted, as we shall see, that the quantity of the serous fluids
may be very variable in the different acute diseases; that the serous
membranes exhale more or less of them, according to the manner in which
they are sympathetically affected.
In the first periods of inflammations, in which the exhalants of the
serous membranes are full of blood which is preternaturally introduced
into them, the serum does not ooze in greater quantity from their
free surface. Then as they are on the one hand very sensible, and
very dry on the other, the motions of the organs that they cover are
wonderfully painful. It is in these first periods that adhesions take
place. If they are not formed either on account of the motion, or for
other reasons, and if resolution of the inflammation does not take
place, then happens to the serous surfaces what happens to a wound not
united; they suppurate, but this suppuration is never attended with
ulceration or erosion of their substance. However abundant the purulent
collections may be, these membranes always remain sound; their texture
is only more or less thickened; pus is thrown out by them, like the
natural serous fluids, that is by exhalation. We know how much this
fluid varies in consistence from milky serum, to the thickest false
membrane that adheres strongly to the surface that has exhaled the
materials of it.
The nature of the fluids of the serous system is very evidently
albuminous. The instant one of the membranes of this system is
plunged into boiling water, I have observed that it is covered with a
white layer which is concrete albumen, and which being removed some
time after, leaves the surface nearly of its original colour. All
the substances which coagulate albumen produce a similar layer upon
the serous surfaces. The experiments of Hewson, who has collected
some spoonsful of these fluids in the great animals, confirm their
albuminous nature. Rouelle and Fourcroy who have analyzed the water
of dropsies have also found albumen predominant in it. Observe upon
this subject that all the white flakes swimming in this water, that
the false membranes that form in it and the white fluids which give it
the appearance of milk, appear to be only albumen which is found in
different degrees of consistence. It might be said that the heat of
inflammation has produced the same phenomenon during life, that common
caloric does upon the white of an egg, the water of dropsies, &c. I
shall not treat of the other accessory principles that enter into the
composition of the serous fluids.
ARTICLE SECOND.
ORGANIZATION OF THE SEROUS SYSTEM.
The first characters of the structure of these membranes are a white,
shining colour, less brilliant than that of the aponeuroses; a variable
thickness, very evident upon the liver, the heart, the intestines,
&c. hardly discoverable upon the arachnoides, the omentum, &c.; a
remarkable transparency whenever these membranes are raised for a
considerable extent, or are examined where they are detached on both
sides, as on the omentum.