becomes a load and a drag, impeding the respiratory movements, making exercise painful, and dulling the sensibilities, it is then not only a source of great discomfort, but the precursor of positive disease.
In a perfectly healthy individual, no abnormal deposition of fat can be supposed to take place, at any age or in any locality, provided the natural appetites and muscular powers be regulated as they ought. Whenever, therefore, we see an individual unnaturally fat or lean, we may safely conclude that an error exists somewhere, and that such an individual either inherits a morbid propensity, or is producing for himself such a propensity.
The conditions which appear to favor an excessive deposit of fat are the following: First, an inherited tendency which predisposes to corpulence, yet always requiring the influence of some exciting cause to bring it into activity. No one can doubt that certain families have a natural tendency to corpulence, which can be often traced through successive generations. It is curious, also, to observe how this tendency is varied in different families, and even in different individuals of the same family. Thus, in one family, we see that the children and females possess a striking tendency to embonpoint, while the male adults, particularly in advanced age, are remarkable for their leanness. In another family, directly the reverse may be observed, the children and females are lean and squalid, while the middle-aged male adults are conspicuous for their corpulence.
Climate and locality seem also to exert considerable influence on the deposition of fat. The inhabitants of low, swampy situations, in temperate climates, are usually remarkable for their bulky flabbiness, and propensity to corpulence; while the inhabitants of very hot and of very cold climates, as well as the inhabitants of mountainous regions, have, perhaps, less tendency to obesity. There is this remarkable difference, however, between the dwellers in hot, and in cold climates: those living in hot climates rarely become fat, without becoming otherwise diseased; while the people of cold climates seem not only to derive protection against the influence of external cold by the layer of fat with which their bodies may be enveloped, but the carbon of the fat, combining with oxygen during the process of secondary assimilation, has with some reason been supposed to contribute to the production of animal heat.
But, of all the agencies which influence the deposition of fat, probably diet and exercise are the most important. Foods have been divided, according to their composition, into nitrogenous and non-nitrogenous. The former, including albumen, fibrine, and casein, consist of only carbon, hydrogen, oxygen, and nitrogen, with some minor ingredients; the latter, embracing starch, sugar, and the fats, are made up of only carbon, hydrogen, and oxygen. It has been thought that the nitrogenous foods are consumed chiefly in the formation of the tissues, while the non-nitrogenous are devoted mainly to the function of
