it is thick, to raise from the cellular layers, but which can never
be neatly divided into two or three portions; a character essentially
distinct from those of the mucous membranes. The action of a blister
on their external surface first laid bare, for example, on a portion
of intestine drawn out in a living animal, does not make a pellicle
rise upon it, as upon the skin, a pellicle under which the serum is
collected. I have frequently made this attempt. What is the immediate
structure of this single layer of the serous membranes? I shall now
examine it.
I. _Cellular Nature of the Serous Texture._
Every system is in general, as we have thus far seen, an assemblage,
1st. of common parts, which are especially the cellular texture, the
blood vessels, the exhalants, the absorbents and the nerves, which
form as we have said the outline and the frame of it, if I may so
express myself; 2d. of a peculiar fibre formed by a substance which
is deposited in this outline, by gelatine, for example, for the
cartilages, by gelatine and phosphate of lime for the bones, by fibrin
for the muscles, &c. That which makes these organs resemble each other
then is the cellular organ, the vessels and the nerves; that which
distinguishes them, is their peculiar texture, which depends itself
upon a peculiar nutritive matter. A bone would become a muscle, if,
without changing its texture at all, nature had imparted to it the
faculty of secreting fibrin, and of encrusting itself with it, instead
of separating the phosphate of lime and being penetrated with it. But
the serous system does not appear to have in it a distinct nutritive
matter, and consequently a peculiar texture. It is only formed of the
mould, the outline of others, and is not penetrated by a substance
that characterizes it. Almost wholly cellular, it does not differ from
this system in its common form, except by a degree of condensation, by
an approximation and union of cells which are found scattered in the
ordinary state.
The following are the proofs that the texture of the serous system is
wholly cellular. 1st. There is an identity of nature where there is
an identity of functions and diseases; now it is evident that the uses
of these membranes and of the cellular texture, as it respects the
continual absorption and exhalation of lymph are completely the same,
and that the phenomena of the various dropsies are common to them,
with the difference only of the effusion in the one and infiltration
in the other. 2d. The inflation of air into the texture subjacent to
these membranes terminates by bringing them almost to a cellular state,
when it succeeds and is pushed for some time; an experiment which is
frequently very difficult. 3d. Maceration, as has been remarked by
Haller, produces at length the same effect, but in a still more evident
manner. 4th. The various cysts, hydatids, &c. whose appearance, texture
and nature even are entirely the same as in the serous membranes, as we
have seen, always arise in the midst of the cellular texture, grow at
its expense and are wholly formed of it. 5th. No fibre is found in the
serous membranes; a character that distinguishes it from all the other
organs and analogous to that of the cellular texture.
To these various proofs of analogy, of identity even of the cellular
and serous systems, we can add the action of different reagents, which
give results precisely similar in both. 1st. Every serous membrane
when dried, becomes transparent, does not turn yellow like the fibrous
and the mucous membranes, preserves a pliability foreign to these
membranes when dried, and gradually resumes its original state when it
is immersed in water. 2d. It becomes putrid much slower than the mucous
surfaces, the muscular layers, the glands, &c. This is remarkable in
the abdomen, upon the peritoneum which is frequently almost untouched,
when every thing is putrid around it, as may be seen by removing it;
for its transparency would make you believe at first view that it was
altered, if you examine it upon the fleshy and mucous surfaces. 3d.
Maceration at the ordinary temperature of cellars, reduces with great
difficulty to a pulp the serous membranes. The omentum, the finest
and most delicate of these membranes has resisted it for a very long
time in my experiments. This phenomenon is particularly striking when
compared with the maceration of tendons which are so resisting, and
which support such great efforts during life. These become pulpy in
water before the omentum is touched. The same phenomenon takes place
with regard to all the other serous surfaces. 4th. In boiling water,
these surfaces acquire the horny hardness like the fibrous system,
but furnish infinitely less gelatine; they do not become yellow like
it. The pleura in those portions of the thorax of animals that are
brought to our tables, has almost its ordinary appearance; only it
is less shining, has lost the faculty of crisping from the action of
caloric, is no longer affected in the same way by acids, &c. If it was
of a fibrous nature it would have disappeared in gelatine, on account
of its delicacy. I shall say the same of the external membrane of the
spleen, the liver and the lungs. Compare these membranes, that are
brought to our tables, when boiled with the intermuscular aponeuroses,
the tendons, &c. you will see that it is impossible to confound, as has
been done, all the white textures together, in regard to their nature.
If we compare the different effects of agents the most known upon the
serous system, with those that we have observed upon the cellular
system, we shall see that they are entirely the same; that these two
systems are consequently analogous, and even identical.
The serous system when it putrefies in the open air does not become
green like the skin, but is of a dull and very deep grey. During life,
on the contrary, its blackness is very evident in gangrene which is
sometimes the result of an acute inflammation, sometimes of those
chronic inflammations, attended with many small white tubercles, which
are so frequently found upon these membranes. This difference arises
from the circumstance, that in the dead body these surfaces are not
penetrated with blood at the time they become putrid; whereas they
contain much during life, when putrefaction succeeds inflammation which
has filled the exhalants with it. Many other facts prove, that the
greater the quantity of blood there is in a part when it putrefies, the
more livid and black it becomes. In the many dead bodies that I have
opened, I have never yet observed gangrene except in the peritoneum.
I have never seen it in the pleura, the arachnoides, the pericardium,
the tunica vaginalis; it no doubt takes place in them; but I think I
have opened dead bodies enough to allow my observation to establish as
a general principle; that the peritoneum is more subject to it than all
the other analogous organs.
Though the different considerations offered above establish much
analogy between the cellular and the serous systems, they exhibit
however real differences. First their external appearance is not
the same. Then there is something in their intimate nature that we
are unacquainted with, and which differs also; for whenever two
organs are identical in their nature, they are subject to the same
affections; now there is a disease of the serous surfaces that is not
seen in the cellular system; it is those slow inflammations of which
I spoke just now, a disease which should not be ranked in the class
of the phlegmasiæ, and which the production of the small tubercles
that attend it, especially characterizes. Authors who have not
sufficiently attended to it, have denominated it chronic enteritis in
the peritoneum, latent inflammation in the pleura, &c. though however
foreign to every subjacent organ, except in the latter periods when it
is propagated by the cellular texture, it has its seat exclusively in
the serous membranes, and is an affection peculiar to these membranes,
as miliary eruptions are to the cutaneous surfaces, as aphthæ to the
mucous surfaces, &c. Add to this difference that of the pus which the
cellular texture and the serous surfaces secrete; this fluid is not the
same in the two systems. The difference of its nature is not known; but
its external appearance is by no means the same.
II. _Parts common to the Organization of the Serous System. Exhalants._
A very evident exhalation is constantly going on upon the serous
surfaces. A particular order of vessels is the agent of this
exhalation, the matter of which is the fluid mentioned above. These
vessels are very distinctly demonstrated in this system; it is the
only one in which the eye of the anatomist can accurately trace them.
The following are the means of seeing them; 1st, in a living animal,
draw out an intestine from the abdomen; it will have a reddish tinge
owing to the vessels under the serous coat, and hardly at all to the
vessels in this coat itself. Irritate it, and reduce the intestine
after attaching a string to it, as in the operation of hernia where
there is gangrene, draw it out again at the end of six and thirty or
eight and forty hours; it will exhibit many reddish lines, running over
this serous surface, and showing in it plainly the exhalants which
were insensible in the natural state, on account of the transparency
of their fluids. 2d. Very fine injections cover in an instant all the
serous surfaces with an infinite number of lines of the colour of the
injected fluid, lines which are evidently exhalants full of this fluid.
3d. In these injections an extremely fine dew is made to ooze out upon
the smooth surface of the serous membranes, a dew which takes place
without rupture or transudation, and of which the exhalants are the
sources. 4th. If a serous surface is laid bare in a living animal, and
wiped dry, it is soon after covered with new serum, which the exhalants
furnish.
_Absorbents._
From the texture of the serous membranes, it is evident that the
lymphatic system enters essentially into their formation, and that
they are probably only a net-work of exhalants and absorbents; for we
have seen that the cellular organ is an assemblage of them. But this
assertion which analogy dictates is also supported by direct proofs.
1st. The fluid of the dropsies of the different cavities varies
in density and colour; now Mascagni has always observed that the
lymphatics in their neighbourhood contained a fluid exactly analogous.
2d. The same author has found in two dead bodies, with a sanguineous
effusion in the thorax, the absorbents of the lungs loaded with blood.
3d. In a man who had become emphysematous after having been poisoned,
these vessels were distended with air. 4th. Coloured fluids injected
into the abdomen or thorax are soon after found, it is said, in the
neighbouring lymphatics, with the same colour. I have often repeated
this experiment; the injected fluid has been soon absorbed, but not
the matter which coloured it; so that this matter, more condensed
after absorption, tinged the serous surface, the lymphatics being as
transparent as usual. It is necessary in general to choose the abdomen
for these experiments, because the absorbents being much exposed on
the liver, can be more easily examined there. This absorbent faculty
is preserved some time after death; but care should be taken, in
order to obtain then the effect more certainly, to keep the animal,
if a warm blooded one, in a bath of nearly its own temperature; I
have had frequent opportunities of being convinced of this truth, and
of observing with Cruickshank, that what Mascagni has said upon the
absorption of dead human bodies, fifteen, thirty, forty-eight hours
even after death, is at least very much exaggerated. 5th. The following
experiment I make every year to demonstrate the absorbents; I macerate
for five or six hours the heart of an ox in water; at the end of this
time, the serous membrane of this organ, which hardly allowed these
vessels to be perceived, appears to be covered with them. 6th. When the
serous membranes are inflamed, the subjacent lymphatics are distended,
like them, by the red globules of blood, &c. &c.
It appears then to be demonstrated, 1st, that the absorbents open by
an infinite number of orifices upon the serous membranes; 2d, that
their origins a thousand times intermixed with each other, and with the
orifices of the exhalants, contribute especially to form their texture;
3d, that the difficulty of distinguishing the absorbent and exhalant
pores is no reason for denying their existence, this difficulty arising
from their extreme delicacy and from the oblique direction in which
they open between the layers of these membranes; thus the obliquity
of the insertion of the duct of Warton, and of the ductus choledochus
even would render the inspection of them very difficult, though these
ducts were infinitely larger; 4th, that from this structure, the serous
membranes, always arranged as we have seen in the form of sacs without
an opening, should be regarded as great reservoirs between the exhalant
and absorbent systems, in which the lymph in going from one remains
some time before entering the other, in which it undoubtedly undergoes
various preparations of which we shall always be ignorant, because it
would be necessary to analyze it comparatively in these two orders
of vessels, which is almost impossible, at least for the first, and
finally in which it serves different uses relative to the organs around
which it forms a humid atmosphere.
_Blood Vessels._
Do blood vessels enter into the structure of the serous membranes?
These vessels are very numerous around them, as is seen in the
peritoneum, the pericardium, the pleura, &c.; they wind upon their
external surface and ramify there. But I have always doubted whether
the greatest number of those which are thus contiguous to them, really
make a part of their texture, and I am even convinced of the contrary.
The following considerations support my opinion. 1st. When these
vessels are injected, they can be easily raised with a scalpel from the
external face of these membranes, without injuring their continuity,
which can never be done in the fibrous or mucous membranes. 2d. No
blood vessel is discoverable on these membranes which are free on
both faces. The arachnoides at the base of the cranium furnishes an
example of this. 3d. The vessels frequently change relations with these
membranes. I have proved above that when the omentum is applied to the
stomach when it is full, the vessels that are between its layers, do
not mount with it upon this viscus, on account of the great stomachic
coronary which opposes it. When dead bodies having large hernias are
injected, the vessels that wind in the ordinary state upon the surface
of the peritoneum which corresponds to the ring, are not seen extending
below upon the hernial sac. Certainly the vessels that are observed
in the broad ligaments of the womb, do not follow them in the great
displacements they undergo in pregnancy.
I think it then very probable that the serous membranes have but very
few blood vessels; what are called arteries of the peritoneum, the
pleura, &c. are but trunks winding on their external surface, capable
of abandoning it when they are displaced, being as it were foreign
to them, not entering immediately into their structure, to which the
absorbent, exhalant and cellular systems almost alone contribute. No
doubt communications exist between the arterial system and the serous
membranes, by means of the exhalants; but nothing precise is yet known
upon the nature, arrangement, and to a certain extent even, the
functions of these vessels.
III. _Varieties of Organization of the Serous System._
We have seen the mucous system exhibiting in each part where it is
found, numerous differences of structure and varying in each region
and in each organ. The serous system varies also, though less than the
preceding. 1st. Each membrane has its peculiar structure. Compare for
example, the arachnoides and the peritoneum; the one fine, delicate
and transparent, yields to the least effort, has no resistance, tears
almost as soon as it is touched, never remains whole at the base of
the cranium, where it is free, if the brain is raised ever so little,
and has, when pressed between the fingers, a remarkable softness. The
other, thicker and more compact, bears without breaking all the efforts
imparted to the abdominal viscera; it can be pulled with impunity. Its
texture is wholly different. 2d. The different portions of the serous
membranes have not the same organization; the omentum is for example
evidently dependant upon the peritoneum and yet it does not resemble
it. I have observed that the intestinal portion of this membrane is
much more delicate than its hepatic, mesenteric portions, &c. That
the half of the tunica vaginalis which lines the albuginea and is
identified with it, is certainly not the same as the half which is
free on the side of the dartos muscle. I cannot say precisely in what
these differences consist; but the external appearance is sufficient to
establish them.
Ought we then to be surprised, if all the serous surfaces are not
equally subject to the same diseases; if inflammation attacks them
with such different degrees of violence; if it takes place ten times
upon the pleura to once that it appears upon the arachnoides; if in
the pericardium, the tunica vaginalis and the peritoneum, it does not
exhibit the same symptoms; if dropsies vary also wonderfully in each;
if the slow inflammations attack them differently, &c.? The pericardium
is subject to an affection which I have seen upon no other serous
surface, and which is yet extremely frequent upon this; I refer to
the white layers, more or less broad, that are formed on its internal
surface, which would be thought at first view to belong to its texture,
which can however be raised from it leaving it sound. I do not know
whence these layers come; do they correspond to the false membranes of
the pleura?
Neither should we be surprised at what has been said of the varieties
which the same membrane exhibits in its diseases. Frequently the whole
of the peritoneum is diseased, and the omentum remains sound and vice
versa. The layers of which I have just spoken are seen upon the cardiac
portion, and not upon the free portion of the pericardium.
Observe however that all the diseases of this system have a common
character which is evidently derived from the analogy of organization.
This and the synovial are the only ones in which large serous
collections take place, in which slow and tubercular inflammations
are formed. The most of their modes of adhesion belong only to
the serous system. Inflammation has a peculiar and distinctive
character in it, of which all the serous membranes partake with some
modifications. The inflammation of the meninges had been classed among
the serous phlegmasias, from the analogy of the symptoms, before I
had demonstrated that the arachnoides, one of these meninges, belongs
essentially to the serous system. It is on account of this membrane,
and not on account of the dura-mater which is of a fibrous nature, that
phrenitis should be referred to the diaphanous membranes.
ARTICLE THIRD.
PROPERTIES OF THE SEROUS SYSTEM.
I. _Properties of Texture. Extensibility._
The serous membranes are endowed with an extensibility much more
limited, than the enormous dilatations of which they are capable in
certain cases, would at first lead us to believe. The mechanism of
their dilatation evidently proves it. This mechanism depends upon
three principal causes; 1st, upon the development of the folds that
they form, and this is the most powerful of the three causes. Hence
why the peritoneum, which of all the membranes of this class, is the
most exposed to dilatations, as from pregnancy, ascites and visceral
enlargements, more frequent there than elsewhere; hence, I say, why
the peritoneum exhibits so great a number of these folds, such as the
mesentery, the mesocolon, the mesorectum, the two omentums, the fatty
appendices, the fold of the cæcal appendix, the broad ligaments of
the womb, the posterior ones of the bladder, &c. &c. Hence why also
these folds are seen around organs subject to habitual alternations of
dilatation and contraction, as around the stomach, the intestines, the
womb and the bladder; very evident in the second state, but slightly
apparent in the first. 2d. The enlargement of the serous cavities
belongs to the displacements of which their membranes are capable. Thus
when the liver is considerably enlarged, its serous membrane increases
its extent in part at the expense of that of the diaphragm, which being
drawn is detached and applied upon the enlarged viscus. I have seen,
in an aneurism of the heart, the pericardium which had been able to
yield but very little, detached in part from the portion of the great
vessels which it covered. 3d. Finally, the texture of these membranes
undergoes a real distension and elongation. But it is in general the
least sensible cause of the enlargement of their cavity; it is only
in the great enlargements that it has an evident influence; in common
cases, the two first causes are almost always sufficient.
I will make an important remark upon the subject of the displacements
of which the serous membranes are the seat in the motions of their
respective organs; it is that these displacements are very painful when
these membranes are inflamed. When the dilated intestines separate the
two diseased layers of the mesentery to lie between them, when the
stomach goes between those of the omentum, &c. when the peritoneum
is inflamed, the patient suffers much. Hence why flatulence is then
so painful, why it is then necessary to avoid taking at once a great
quantity of drink. We know the acute pain that a long inspiration
produces in pleurisy; it is because the lungs then dilate the pleura,
and tend to go between the folds which accompany the great pulmonary
vessels.
_Contractility._
It corresponds with the extensibility; it is less consequently than it
at first appears to be. When the peritoneum for example is contracted,
its different folds are formed; it returns to its place after having
experienced locomotions. But it cannot be denied that in great
dilatations these two properties are very sensible; for example, in
hydrocele as the water is evacuated, the tunica vaginalis evidently
contracts. The peritoneum after the paracentesis of the abdomen
exhibits the same phenomenon. At the time of performing the operation
of empyema, the pleura does not experience it so sensibly, not from
defect of contractility, but because on the one hand it adheres to the
ribs which do not contract, and on the other if the effusion is of
long standing, the lungs are so flattened by the pressure, that the
air can no longer dilate them, so that there remains a space between
the costal and pulmonary portion, which is filled with air. A similar
space would also remain at the moment of the operation, if the serum of
hydrocephalus was evacuated.
After long distensions, the serous membranes no longer contract;
the tunica vaginalis remains flaccid after frequent punctures, the
peritoneum after frequent pregnancies, &c. &c.
II. _Vital Properties._