The cellular membrane. It is called tela cellulosa, panniculus adi-posus; membrana adiposa, pinguedinosa,et reticularis; in French, tissue cellulaire, tissue muqueux,and Iorgane cellulaire. This membrane is of the greatest extent, and of the utmost consequence in the human structure; for it connects and penetrates into every part; indeed it seems to be the very constituent of most, if not all, the parts that are called the solids in our bodies. Experiments prove that all membranes, without exception, and the vessels, which are hollow membranes, the parenchymatous substance of the viscera, ligaments, and a great part of the bones, either are or have been cellular texture. The cellular membrane, when compacted in different degrees of density, forms these solids. Air introduced under the skin diffuses itself through all the surface of the body, penetrates into the interstices of the muscles; and Haller asserts, that even the vitreous humour of the eye hath received the flatus of an emphysema.
Some describe the cellular membrane not as one, but as a congeries of many membranous lamina joined irregularly to each other at different distances, so as to form numerous interstices of different capacities, and which communicate with each other. These interstices they call cellulae, and the substance made up of them cellular substance.
It is generally and properly considered as of two kinds, viz. reticular and adipose; and the latter is described as a connection of fibres, forming, by their different directions, cells for the lodgment of oil or fat. In some parts its substance is merely a net work of slender fibres, which give it ductility and looseness; for instance, under the skin of the penis and scrotum. In other parts it is more or less loaded with oil, and is less porous or spongy in its substance, as under the skin of the buttocks, and in the soles of the feet. Dr. Hunter uses the term cellular as the generical name, and the names reticular and adipose for expressing the two species. He also observes, that the reticular part is evidently dispersed through the whole body, except, perhaps, in the substance of the bones, of the brain, and in the humours of the eye; that it is found in a much greater degree in the belly of muscles than in the tendons, in which it is scarcely discerned. He is also of opinion that the adipose membrane is composed of two kinds of cells; viz. the reticular, which communicate with each other; and adipose, which are distinct, and are the reservoirs of the animal oil, or a white granulated matter, capable only of being fused by heat; the cells of which are called sacculi adiposi. He urges, as a proof of his opinion, that the water in an anasarca goes downward while we are in an erect posture, but the oil does not. The oil is supposed to be secreted by the small arteries, and occasionally absorbed into the circulation. Dr. Hunter thinks that wherever there is fat in the human body, there is a particular glandular apparatus superadded to the reticular membrane, consisting of vesicles, or bags, for lodging the animal oil, as well as vessels fitted for its secretion.
Whether or no the cellular membrane be the basis of all the organized and vascular parts of our frame, Dr. Hunter hath proved that the most simple parts of it are vascular; that the callus, which unites broken bones, is itself bone, and also vascular; that the morbid adhesions, between different adjacent parts, are vascular, and that a cicatrix in the skin is vascular. He infers from hence, that all our solids are organized; and that, whether lengthened or renewed, they shoot in a vascular form. But here he speaks of the visible parts. We suspect, however, that the importance of this connecting reticular texture has been greatly exaggerated. We see in it nothing but connecting threads, which any condensed glutinous substance forms; and, if the cells communicate through the whole body, it is no more than may be expected from the union of different separate organs. If these are united in one part, they are separated in another; and we can easily see that by some passage all may communicate.
It has been said, that membranes are formed of this substance. We know that, when condensed, it will assume a membraneous appearance; but we have no evidence of it in any case possessing nerves or organization, like what we may style primordial membranes. The effused gluten, between the pleura and lungs, assumes this form; but we cannot say that this is an organized substance. The cellular texture never appears to be vascular: even in a state of inflammation it is never sensible. It is the seat of an abscess, but is not itself inflamed. Nerves pass through it, but are never lost on it. The former editors of this work have suggested, that it may be formed from the coats of the nerves; but these are never deposited except at their minutest extremities, where the nervous power acts with its peculiar functions. This never occurs in the cellular substance, except of the muscles; and it would be a gratuitous assertion, that such was the origin of the cellular substance in muscular flesh, when, in every other part of the body, no such source could be traced. In fact, we see in every part of the cellular substance only hardened gluten, without either a nervous or glandular apparatus. Whether the adipose membrane differs in its structure we doubt. There is some reason to think so: but we must remember that, if one part of the cellular substance be filled, the surrounding membrane is thickened; and this will account for the retention of the fat in those cells where it is deposited. Among the uses of this membrane, the following are sufficiently obvious.
1. It fills up interstices, and gives an agreeable contour to the body. Vol I.
2. It is a cushion to defend against pressure, hence it is of a thicker composition in infants.
3. It connects the parts of the body, but so as to admit of a sliding motion between them.
4. In some parts of the body it serves as a bed for more tender organs; as in the orbit and scrotum, as well as a reservoir for animal oil.
This membrane is the seat of abscesses, the leuco-phlegmatia, emphysema, anasarca. In a consumption it is shrunk up so as to be hardly visible; in an anasarca its oily contents are all destroyed; and in an emphysema almost its minutest parts are rendered visible.
On this article, see what Dr. Hunter says in the Lond. Med. Obs. and Inq. vol. ii. p. 26, etc. Haller's Physiology; Malpighius on the Cellular Membrane; Dr. Shebbear in his Theory and Practice of Physic; also Recherches sur le Tissu Muqueux, ou lorgane Cellulaire, par Mons. Theoph.de Bordeu.