Part 12

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.

All have but a single layer which it is possible, at the places where 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._