The uses of the fat deposited beneath the skin are, first, to protect the body from external shocks by a uniform diffusion of pressure through the whole adipose tissue; and, second, to keep up the heat of the body, by materially checking, through its very slight conducting power, the loss of free heat by radiation. This use of the fat is most clearly seen in some of the lower animals (the seal, whale, etc.), which are exposed to very low temperatures.
Another physical use of fat is to promote the mobility Of-Various organs. Hence, in cases of extreme emaciation, it always remains in the parts where motion is most essen tial, as the heart, and the orbit of the eye.
Another of its important physical properties is that of rendering other bodies supple, and diminishing their brittleness. In this point of view, the use of fat is very conspicu ous in the bones.
The chief chemical use of the fat is its power of exciting and supporting the animal heat. In the oxidation of the fats in the animal organism, whether the process be gradual or rapid, a large amount of heat must necessarily be liberated; and that they are oxidized, and for the most part reduced to carbonic acid and water, is evident, because they neither appear in any quantity in the excretions, nor, as a general rule, accumulate beyond a certain point in the organism. An accumulation of fat thus serves as a reser
voir of combustible matter in time of need. This is especially evident in time case of hybernating mammals, as, for example, hedgehogs, in which an enormous quantity is deposited just before the hybernating period: during this period, it gradually disappears, its carbon being slowly consumed in the respiratory process, and keeping. up the animal heat.
Frit is, moreover, one of the most active agents in the metamorphosis of animal mat ter. Lehmann ascertained that a certain, although a small quantity of fat was indispen sable to the complete gastric digestion of nitrogenous food, a fact which is confirmed by the observation that in experiments on artificial digestion, the solution of substances used as food is considerably accelerated by the presence of a little fat. The occur rence of fat in the milk and in the egg, as also in all highly cellular organs (as, for example, the liver), is a clear indication that this substance plays an important part in the process of cell-formation; and no animal cell or cell-yielding plasma has ever been observed in which fat is not a constituent.
An undue accumulation or increased growth of the fatty tissue gives rise to the con dition known as obesity (q.v.).