Adipose Substances (Lat. adeps, fat), a class of substances of a fatty nature, which are present in greater or smaller quantity in most animal and vegetable organisms. Adipose substances are all composed of carbon, hydrogen, and oxygen, to the exclusion of other chemical elements. They are all crystallizahle at a low temperature and fluid at a high temperature, combustible, and insoluble in water, but soluble in ether and in each other. They differ from each other in the exact proportion of the different chemical elements which they contain, and particularly in the precise degree of temperature at which they crystallize or assume the solid form; some of them, such as stearine when pure, remaining solid above 140° F., while others, such as oleine, continue fluid until near the freezing point of water. The three special kinds of adipose substance with which we are most familiar are stearine, margarine, and oleine; stearine and margarine being the principal constituents of the more solid fats, while oleine is abundant in the more fluid fats, or oils. In the animal body, these different substances are usually mingled with each other in various proportions, thus forming fats or oleaginous ingredients of different degrees of consistency.
They are found in the adipose tissue, of which they form by far the largest part; in the minute cells of the liver and of some cartilages, where they are deposited in the form of microscopic globules; in the brain and nervous matter, where they are found in the proportion of from 5 to 15 per cent.; in the marrow of the bones; in the chyle, to which fluid they impart its opacity and white milky color; and in the milk itself they exist under the form of the milk globules, which are minute particles of butter, formed of a mixture of various tatty substances, and suspended in the serous fluids of the secretion. There is also a sebaceous matter secreted by the skin, especially in the parts covered with hair, which is a semi-solid or lardaceous secretion, consisting largely of adipose materials. Fatty substances also exist in considerable abundance in the food, since they enter so largely into the composition of animal and vegetable tissues. The fat of meat, the liver and the brain of animals, when used as food, of course supply a large quantity of adipose substances.
Milk and butter and the yolk of eggs are especially rich in these materials; and many articles of vegetable food, such as nuts, olives, Indian corn, etc., also contain them in large proportion. - Although fatty substances by themselves are not capable of sustaining life when used exclusively as articles of food, yet they are extremely useful and perhaps indispensable as part of the regimen. This is shown by the instinctive desire, which is nearly universal among healthy persons, to have some kinds of adipose materials as a portion of the food; butter, fat, and olive oil being the kinds most highly valued and abundantly used. It has also been proved directly by the experiments on the fattening of animals by Boussin-gault (Chimie agricole), who found that, however abundant and appropriate the other elements of the food might be, the addition of a small quantity of fatty substance improved greatly the condition of the animals, and caused the formation in their own bodies of a much larger amount of fat than that which had been introduced. Thus the fat which exists in the interior of the body of a living animal has not all been derived from similar materials taken with the food.
On the contrary, there is every reason to believe that fatty substances are produced in some way, in the process of digestion and assimilation, from the starchy and saccharine elements of the food. It is a matter of common observation that food containing an abundance of starch and sugar is especially favorable to the deposit of fat; and Boussingault also found that the most effective diet for the fattening of pigs was one consisting very largely of cooked starchy materials, with the addition of a small proportion of fatty substances. The adipose substances found in the body are thus partly introduced with the food, and partly generated from the transformation of its starchy and saccharine ingredients. They are then deposited in the various tissues, or form for the time a part of the fluids or secretions, like the chyle, the milk, and the sebaceous matter of the skin. Of all the fatty material thus taken with the food, or generated in the system, but a small part is again discharged in its own form. It is only the fat of the sebaceous matter and that of the milk which is thus discharged. The remainder is decomposed or transformed in some way in the daily process of nutrition, so that it is no longer recognizable as fat.
In the opinion of some writers, it is directly oxidized by the air taken in by respiration; thus producing animal heat and the evolution of carbonic acid, as it would do if burned, as in the case of ordinary combustion. But this must be considered as doubtful, since we cannot yet follow all the details of the chemical changes which take place in the living body. It is certain, however, that the fat which is taken up from the intestine during the digestion of food is absorbed by the vessels, partly deposited in the adipose and other solid tissues, and for the most part rapidly decomposed or transformed, so that it disappears and is used up, so to speak, in the nutrition of the body.