FATS (AS. feet, Icel. feitr, Dutch ret, OHG. feizit, Ger. feist, Felt, fat). An important class of substances found in all parts of the animal organism, although they occur mainly in sub cutaneous tissue and on the surface of muscles. They are largely taken in ready-formed in the food. Unlike the albuminoids, however, they are also to some extent produced by the animal or ganism itself. As to their mode of formation, it was for a long time believed that they are de rived in the body from sugar, starch, and other carbohydrates; in recent years, however, it has been shown that they are produced by the chem ical transformation of albuminoids, though the presence of carbohydrates does seem necessary to their formation. The quantity of fat in the human body varies considerably at different peri ods of life. In the earlier stages of fatal exist ence we find scarcely any fat; in new-born chil dren there is usually a considerable quantity of this substance deposited under the skin, and the organism continues rich in fat till the age of puberty, when a marked diminution of the sub stance occurs. It again increases about middle life, and then occasionally occurs in great excess; for example, three or four inches of fat are not infrequently found under the skin of the (tb• domen of corpulent persons. Extraordinary de• posits of fat in some particular part of the body are sometimes found both in men and in animals; the remarkable prominence of the buttock in Hottentot W011101 is due to this cause. The uses of fat in the animal organism are manifold. It plays au important part in the process of cell formation ; it protects the holy from external shocks by a uniform diffusion of pressure through the whole adipose tissue; it checks the loss of heat by radiation; it promotes the mobility of various organs, etc. Its chief use, however, con sists in supplying a great part of the heal energy indispensable to animal life, heat being produced in the organism mainly by the combustion of available fat. A moderate aeetnnidation of fat serves as a store of eombustible matter in time of need. A superfluous growth of fatty tissue,
on the other hand, is a source of great uncoil venience, and gives rise to the condition known :IS obesity. See also DEGEstaRATION.
The fats are lighter than water; when brought in contact with paper or fabrics they leave a translucent yrcase-spot. which is generally very difficult to remove, though it can sometimes be washed out with ether, benzine, chloroform, oil of turpentine, and other organic liquids in which the fats are soluble. To determine the amount of fat in milk, cheese, or any other mixture sub mitted for examination, the analytical chemist dissolves out the fat with ether, separates the ethereal solution from the other ingredients, evaporates it. dries the residue, and weighs the pure fat thus obtained in a suitable dish. Fats have the peculiar property of forming emulsions with water, in which the minute globules of fat often remain in suspension for a very long time; milk is such an emulsion. To emulsify fat arti ficially. it is melted, if hard, and simply shaken up with water in which some carbonate of soda has been dissolved.
Besides serving as a necessary ingredient of food, fats are applied industrially to many useful purposes. They are often used as fuel and as illuminants, and very extensively for the manu facture of soap and candles. Formerly they were much used also as lubricants; in this application, however, they have been largely replaced by oil derived from Russian petroleum.
To obtain the fat, the suet from the animal body is pressed between warm plates or kneaded in muslin bags placed in hot water: the fat melts and is readily separated from the animal mem branes. Or else the fat is dissolved out with ether, in which the membranes are insoluble. An other process sometimes employed consists, on the contrary, in dissolving the membranes with di lute acid or alkali, which leaves the fat nnat tacked. The crude fat may be purified by treat ment with sulphuric acid.