Page:The American Cyclopædia (1879) Volume I.djvu/139

ADIPOSE SUBSTANCES combustible, and insoluble in water, but solu- ble in ether and in each other. They differ from each other in the exact proportion of the dif- ferent chemical elements which they contain, and particularly in the precise degree of tem- perature 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, mar- garine, 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 form- ing 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 depos- ited 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 fatty 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 se- cretion, consisting largely of adipose mate- rials. Fatty substances also exist in consider- able abundance in the food, since they enter so largely into the composition of animal and ve- getable tissues. The fat of meat, the liver and the brain of animals, when used as food, of course supply a large quantity of adipose sub- stances. 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, &c., 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 indis- pensable as part of the regimen. This is shown by the instinctive desire, which is nearly uni- versal 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 experi- ments on the fattening of animals by Boussin- gault (Chimie agricole), who found that, how- ever abundant and appropriate the other ele- ments 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 ADIPOSE TISSUE 119 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 pro- duced in some way, in the process of digestion and assimilation, from the starchy and saccha- rine elements of the food. It is a matter of common observation that food containing an abundance of starch and sugar is especially fa- vorable to the deposit of fat ; and Boussingault also found that the most effective diet for the fat- tening of pigs was one consisting very largely of cooked starchy materials, with the addition of a small proportion of fatty substances. The adi- pose substances found in the body are thus part- ly introduced with the food, and partly gener- ated from the transformation of its starchy and saccharine ingredients. They are then depos- ited 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 re- mainder is decomposed or transformed in some way in the daily process of nutrition, so that it is no longer recognizable as fat. In the opin- ion of some writers, it is directly oxidized by the air taken in by respiration; thus produ- cing 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 con- sidered 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. ADIPOSE TISSUE, the tissue in animal bodies containing the largest proportion of adipose substance, known in ordinary language as the fat of the animal, in distinction from the lean or muscular flesh. The adipose tissue is situ- ated principally beneath the skin and over the muscles, particularly those of the abdomen, about the cheeks, in the orbit of the eye, over the buttocks, on the outside of the heart about the origin of the great vessels, over the intestines, where it forms a special layer or dis- tinct curtain called the omentiim, around the kidneys, and in various places about the- inner side of the abdominal walls. It consists of a number of distinct masses or lobules, which are connected with each other by thin layers of areolar tissue, containing the few blood vessels and nerves with which the adipose tissue is supplied. Each lobule in its turn consists of a number of transparent vesicles, or closed sacs, about yfs of an inch in diameter, which are