The figure of the cells is so variable, that we cannot describe them in a general manner. Round, quadrangular, hexagonal, oval, are found mixed together. The best way to see these, is to freeze an infiltrated limb; numerous little icicles are then formed, and show by their form, that of the cells which they filled. Artificial emphysema is also a good way; I have often determined by it in our slaughter houses where they blow meats, the forms of the cells. The injection of melted gelatine may also be employed; but the results are less certain, because in going from one cell to another, it breaks the texture; and moreover after it is hardened, it is difficult to separate each portion contained in each cell.
All the cells communicate; so that the cellular texture is really permeable throughout the whole extent of the body, from the feet to the head. This permeability is proved, 1st. by emphysema spontaneously produced; 2d. by that which is artificially produced in a living animal, by blowing air under any portion of the cutaneous organ, an operation which affects neither the life or health of the animal, though oftentimes the whole of the body is bloated. We know that some beggars make use of these means without danger, for the purpose of exciting compassion. 3d. If one or two punctures are made in a dropsical limb, it is sometimes wholly emptied in this way. 4th. Oftentimes this happens from ruptures taking place spontaneously in limbs of this kind. 5th. Pressure made upon them, makes the fluid ascend or descend, according to the part upon which it is made. 6th. A rupture of the bladder or the urethra produces an urinous infiltration, which sometimes extends even to the sides of the chest. 7th. The injection of any fluid into the cellular texture of a dead body, produces an artificial leucophlegmasia.
The permeability of the cellular texture has been much exaggerated, or rather it has been presented under a point of view different from that in which it is shown by nature. It is thus that many physicians, thinking that it could be pervaded indifferently by all the fluids of the animal economy, have believed that these fluids formed there, currents in different directions more or less irregular. Thus the sweat has been considered as the transmission by the skin of the albuminous fluid of the cellular texture, which, according to some moderns, is drawn out with the caloric that is constantly disengaged. They have thought, also, that the permeability of this texture would explain the rapid passage of drinks to the bladder. They have explained by it too, the promptness with which sweat is produced by warm liquors, &c.
All these theories, that examination never proves, are repugnant to the known laws of our economy, laws which show us the fluids constantly circulating in the vessels, in consequence of the vital forces, of organic sensibility and contractility which they possess, and not as being extravasated to move irregularly in the cellular texture. Moreover, I have never found any portion of drink in the cellular texture of animals immediately after they have taken it. I have tried many of these experiments upon dogs, after having deprived them for some time of drink, that they might drink the more. The cellular texture in the neighbourhood of the stomach and intestines, that especially which, placed behind the mesentery, communicates with the pelvis where the bladder is situated, having been attentively examined, did not appear to me to contain any fluid; it was analogous to that of the other parts of the body. Besides, as we shall see hereafter, these phenomena can be explained in a very natural manner.
The cellular texture is permeable, then, only to fat and lymph; and yet it appears that but little use is made in an ordinary state of this permeability by these two fluids, which remain in their cells, until absorption takes them up. We do not see them pass from one to another; they are stagnant, if we may so say. It is only in serous infiltrations, in effusions of pus, in one word, in a morbid state, that the cellular permeability becomes apparent. We can only consider, then, the cellular texture as the reservoir, in which are formed the serum and the fat. After death the cellular texture is every where penetrated by fluids, which pass not only across the communicating openings of its cells, but also through the pores which it has, like all the solids; hence the infiltration of the integuments of the back, in dead bodies that have been laid upon it for a length of time; hence also the passage of the bile through the texture, which separates the gall bladder from the duodenum, and by which means this intestine is discoloured, &c. &c. But these phenomena have nothing in common with those that take place in the living body.
II. Of the serum of the cellular membrane.
The first of the two cellular fluids appears to be the same as that which is elsewhere furnished by the exhalants and taken up by the absorbents. The first deposit it in the organs, the second carry it from them. Thus when we expose to the air condensed by cold any part of the cellular texture of an animal recently killed and still preserving its heat, we see a vapour arise which results from the solution of the serum in this air, a vapour perfectly analogous to a cloud that transpiration and respiration produce in winter, or even to that which arises from any aqueous fluid, exposed hot, with a large surface to the action of fresh air. When the atmosphere is warm the solution takes place in the same way, but as the vapour is not condensed, there is no apparent cloud.
The cellular serum varies in quantity in the different regions. Where there is no fat, as in the scrotum, the eye-lids, the prepuce, &c. it appears to be a little more abundant than elsewhere. We see also that these parts are much more disposed to different infiltrations. In this respect, the scrotum holds the first rank; then come the eye-lids, afterwards the prepuce, &c. Observe upon this subject, that the cellular texture exterior to the mucous surfaces, the arteries, the veins, and excretories, a texture which by the absence of fat resembles the ordinary, differs from it, however, in this, that serum is never effused in it.
We cannot judge of the quantity of cellular serum by observations made upon the dead body, in which the laxity of the parts permits a transudation of the fluids from all the vessels that pass through the cellular texture, and which then enter the cells. To estimate accurately the cellular moisture, I made an animal first emphysematous below the skin; I made a large incision into this; little blood only escaped, because the swelling separated the vessels from the course of the knife. By these means, the cellular texture being laid open, I have often been convinced that there was much less serum in this texture than we commonly suppose. I have not observed, that during digestion, after sleep, and whilst much sweat is exhaled by the cutaneous organ, three circumstances under which I have repeated these experiments, that the cellular serum is increased or diminished in a sensible manner. This fact coincides with what I have stated in my Treatise on the Membranes, upon the fluid that lubricates the serous surfaces, and the proportion of which is almost always nearly equal.
We know that in leucophlegmasia, the quantity of cellular serum is much increased; that it disappears in inflammation, &c.