In the first place, the fat is subject to considerable deviations from its natural quantity and quality.

Not unfrequently it is found collected in excessive amount, and at the expense of the nutrition of other structures, especially of the muscles. The excess, when uniform throughout the body, constitutes what is expressed by the general term obesity, and to it the female sex is particularly liable: but iN some cases it accumulates at particular spots externally, and disfigures the body; or internally in such a manner as to narrow the space of the cavities of the body, and to interfere with the functions of the organs contained within them. Thus it collects at the lower part of the abdomen, on the nates, and on the loins (in which region the rolls of fat are situated, which distinguish the race of Hottentot women); it is found, too, in the neighborhood and in the cellular interspaces between the lobes of the mammae in women; in the medias-tina, and beneath the pleura; in the folds of the peritoneum; around, and in the duplicatures of, synovial membranes, etc. The local accumulations just mentioned, constitute a sort of transition to the fatty tumor, lipoma. Invested with a cellular sheath, lobulated by interstitial cellular tissue, more or less of which traverses its interior, and resembling adipose tissue in its intimate texture, the fatty tumor chiefly occurs in those regions at which fat is naturally most abundant: it is, however, sometimes found in parts where in the normal state no fat is deposited; as, for instance, in the submucous cellular stratum of the intestinal tract.

Yet more frequently, in the emaciation which attends disease, the quantity of fat existing is found remarkably small, and at certain parts of the body, if not everywhere, it may even entirely disappear.

Moreover, the fat presents various qualitative deviations from its physical, and no doubt also from its chemical, properties. Sometimes it is remarkably pale, and sometimes, on the contrary, of a very dark color; it may be soft, gelatinous, suety, greasy, like the marrow of bones, and oily; or again, firm, and resembling soap or adipocire. Thus in advanced age, and in persons whose muscular system loses energy and bulk, and becomes prematurely aged, the fat is of a deep yellow color and oily; in spirit-drinkers, in persons who are negligent as to the state of their skin, in those whose skin is thick, soft, and dark colored, or in whom the liver is suety, or the heart the seat of fatty metamorphosis, etc, it is usually pale, and resembles mutton suet.

In dropsical patients it is often reddish, firm, and granular, the fat vesicles shrinking together, and forming a reddish firm acinus: but otherwise it disappears, and after it has been absorbed, its place is occupied by a fatty, gelatinous, and, at last by a serous, fluid.

The serum, which in the natural state, is uniformly diffused through the cellular tissue and moistens it, is subject to similar deviations from the healthy condition.

It is almost entirely wanting in cases of considerable general or partial emaciation, in the marked collapse which succeeds convulsive diseases, or when, as in serous diarrhoeas and Asiatic cholera, the serum of the blood is rapidly lost, etc. In these cases the cellular tissue is dry and crepitant, and resembles that of plants. In other instances, again, it exceeds the natural quantity: this excess, when general, constitutes leuco-phlegmasia, hydrops universalis, anasarca; when local it is named oedema. The fluid varies much in color, consistence and composition, according to the processes by which its accumulation has been effected, as well as according to the composition of the blood; being either thin and clear as water; or rather thick, and like jelly, from containing albumen; or yellow, in consequence of the presence of bile; red, from the admixture of more or less blood with it; or turbid, milky, whey-like, and flocculent, from its containing fibrin or purulent matter.

Among the foreign bodies found in cellular tissue are:

A. Gas

Gas; which may be either atmospheric air or some of the various animal gases - windgeschwulst, emphysema. Atmospheric air accumulates in cellular tissue in consequence of wounds in the circumference of the thorax by which the pleura is opened; and more frequently it succeeds penetrating wounds of the lung, fractures of the ribs by which the costal pleura is torn and the lung injured, ruptures of the lung and pleura occasioned by crushing, mortification of the lung and superjacent pleura, ulcers which perforate the larynx and trachea, and laceration of one or more of the air-cells of the lung (from violent coughing, etc.) The emphysema is occasioned either immediately by the entrance of the atmospheric air at the wound of the chest, or by its escape from the air-passages into the adjoining tissue, or into the cellular structure which intersects the lung itself - emphysema pulmonum inter!obulare. When the bowel is perforated either by ulceration or sloughing, its gaseous contents pass out into the cellular tissue: in some cases of mortification gas is spontaneously evolved, and the skin over it swells up, and forms a doughy tumor. Lastly, there are a few cases in which, without any of the above-mentioned causes, gas accumulates in the subcutaneous tissue, and still more frequently in the interstitial, and especially the submucous, cellular tissue of the bowel: such cases result from acute disorganizations of the blood, and are found when there is no trace of cadaveric decomposition in the body. Transient emphysemas of the same kind are well known to occur in the living subject, in consequence of convulsive affections.

B. Blood

Blood; which may be extravasated in consequence of injuries of various structures, either from external or internal causes: the extravasation may be diffused through the tissue, or circumscribed, or even encysted. Purulent matter also may be effused; and, from penetrating wounds, or spontaneous ruptures, or perforating ulcers, of the urinary passages, etc, urine may be extravasated. Lastly, y. All kinds of foreign bodies may be thrust into cellular tissue through wounds of the integuments, or pass into it from the intestinal tube; they sometimes wander further in various directions, and sometimes they fix in the cellular tissue within a capsule of false membrane.