Fat, called also pinguedo, axungia, buty-rum, arvina, arabus, etc. Fat is a condensed oily juice, contained in that part of the cellular membrane called membrana adiposa. When superfluous, and found in the upper eye-lids of children, it was called axirnach. In the young foetus is scarcely any fat; the omentum seems only to contain a jelly; but in the more advanced stage, fat begins to appear. When the child is born, and during a few years after, it hath much fat immediately beneath the skin; in men the fat is most abundantly spread on the glutei muscles: it is separated from the blood by a glandular secretion.
From the most accurate analysis of Crell, it appears that fat is a kind of oil, or butter rendered concrete by an acid. This, the sebacic acid, exists ready formed in suet, two pounds affording somewhat more than seven ounces. By adding alkalis to animal fat, a soap is formed; which is decomposed by alum. We thus obtain the sebate of potash, which is decomposed by the sulphuric acid. When chemically examined, it is found to resemble very nearly the acetous acid. Six parts of fat contain nearly five of carbon, and one of hydrogen, with some of the acid, not decomposed; nor does it yield so much oxygen and nitrogen as the fleshy parts. The accumulation of fat is a process not completely understood; nor are its uses known. It contains, as we have seen, the acetous acid; and, on the whole, seems a morbid secretion when in a large quantity, since it predisposes to many diseases, and is itself a disease. We should suspect that it was designed to in-viscate a proportion of the acetous acid when in excess; since it is favoured by indolence and inactivity, when we find acids morbidly accumulated in different secreted fluids, as in the urinary and arthritic calculi. It has been supposed to be the accumulation of a stock of nutriment, to supply accidental and temporary deficiencies, or to cover morbid acrimony in the fluids. It must be allowed, that, from want of food, the fat wastes and is absorbed; but we arc yet to learn, that fat persons can bear famine better and longer than lean ones. At the same time, it is observed that the fat is not so much wasted in those who are worn down by the gradual decay of a hectic; who, from a scirrhous oesophagus, or a cancer of the throat, die from inanition, as in dropsies, where the appetite continues with little diminution. It has also not been ascertained that it imparts any . to the body, or the viscera, which the omentum covert,.
Berthollet discovered, in animal substances, what he considered as a peculiar acid, and he called it the Zoonic acid. It had the smell of broiled flesh, was liquid in a temperate heat, more volatile than boiling water; formed soluble salts with barytes, strontian,lime, and alkalis; precipitated the nitrat of lead and the acetite of mercury; deposited charcoal, and was, in time, decomposed. Subsequent inquiry has, however, shewn that this is not a new acid, but the acetous acid, containing some animal matter in solution. It is of more importance, since it shews the acetous acid in a new compound in the animal machine.
Fat differs from suet principally in the great quantity of water it contains, which, being slowly evaporated, is converted into a sebaceous substance. Steatoms, which sometimes are found in the membrana adiposa, are of a very different nature.
The human fat does not become fluid when Fahrenheit's thermometer rises to the ninetieth degree; but when it begins to putrify, it easily, and with a small degree of warmth, runs into oil.
In cetaceous fishes the fat is thin as oil; in animals that live on herbage only the fat is harder, and yet harder in those that chew the cud.
The Arabians used a great variety of fats in medicine; but to relax the parts to which they are applied, and to stop perspiration, are their chief virtues. In the present practice, three kinds are employed, and these only on account of their different consistence; they are the fat of vipers, hog's lard, and mutton suet. The fat of geese is now wholly rejected. Their use is chiefly external. As to viper's fat, it is well supplied by the oil of olives; for it does not appear that animal fats, and insipid, flavourless vegetable oils, of similar consistence, differ in their effects when used externally: in other instances, there seems to be a greater similarity between animal and vegetable fats, or insipid oils, than between any other similar animal and vegetable substances, such as gums and animal jellies: animal fats, in their resolution by fire, yield neither the peculiar stench, nor much, if any, of the volatile alkaline salt, which substances completely animalised afford. Mutton suet is sometimes taken internally as. a mild nutrient; occasionally, as a demulcent in diarrhoeas, when the mucus of the intestines is abraded; but it seems to possess no very considerable power in either respect.
Animal fats are not soluble in rectified sp. vin. nor in water. When scented with essential oils, the latter may be totally extracted by digestion in rectified spirit, and, in a less degree, by water. Fats may thus also be freed from their ill smell; and those that are become rancid may be made sweet.
Animal fats preserve steel from rust better than vegetable ones; mutton suet prevents brass from growing ill coloured, longer than any other fat; and if a little camphor and white lead are added, these ends are still better answered.
The fat of vipers being separated- from their intestines, may be melted before a gentle fire, and run through a thin linen cloth.
See Haller's Physiology, on the cellular membrane.