Page:Popular Science Monthly Volume 1.djvu/460

446 himself, with his regular treatise "On Corpulence in Relation to Disease." Dr. Harvey's book is an excellent summary of the subject, and has the weight of professional and scientific authority; the present article is mainly condensed from his pages:

The manner in which fat is distributed over the body is now generally understood to be by the texture of the cellular membrane. Formerly it was thought to adhere in clusters to the parts where it was found—a mistake that has been corrected by the study of minute anatomy. The cellular tissue, as its name implies, is made up of great numbers of minute cells, which communicate with each other, and which are formed by the interlacings of fine, soft, colorless, elastic threads, intermixed with delicate films or laminæ, the tissue presenting, when free from fat, a white, fleecy aspect. This tissue is found everywhere underneath the skin; the serous and mucous membranes are attached by it to subjacent parts; it lies between the muscles, and also among their fibres, surrounds the blood-vessels, and is generally distributed throughout the body. In certain situations, as around the large blood-vessels and nerves, in the omentum and mesentery, about the joints, and especially under the skin, the cells enclose what are known as adipose vesicles, minute spherical pouches, filled with fat or oil; and, when these are present in notable quantity, the structure takes the name of adipose tissue. As thus deposited, the fat appears merely to be held in store, as it remains quite distinct in form and situation from other parts of the animal frame. It, however, enters largely into the composition of nerve-substance, where it becomes an essential part of a highly-organized tissue.

The development of fatty tissue varies considerably at different ages, and in the two sexes. In children and in females, especially in early age, the principal seat of the fatty deposit is in the cellular tissue, immediately under the skin. During adolescence, the fat has a tendency to disappear from this situation; but, about middle age, frequently becomes again deposited, not only in the subcutaneous tissues, but also in the neighborhood of certain internal viscera. The quality of the fat also varies, both with the age and with the part in which it is deposited. It is firmer and higher colored in old persons than in young ones; and is more condensed and solid in parts liable to compression, than in the omentum, or about the heart, stomach, and intestines.

A moderate amount of fat is a sign of good health, and physiologists generally allow that it ought to form about the twentieth part of the weight of a man, and the sixteenth of a woman. Independently of its importance as a non-conducting substance in impeding the too rapid escape of animal heat, fat may also be regarded as a store of material to compensate for waste of tissue, under sickness, or other circumstances, entailing temporary abstinence from food. But when fat accumulates to the extent of interfering with important functions, and