General Anatomy, Applied to Physiology and Medicine, Vol. 3 (of 3)

by Xavier Bichat

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.