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.