Page:Popular Science Monthly Volume 15.djvu/395

 understanding of our subject, a brief sketch must be presented. Let it suffice to say that carbon, hydrogen, and oxygen, the three all pervading elements of the vegetable world, enter largely into the composition of the animal body; and that the two former especially constitute a fuel the oxidization of which produces animal heat, and develops the force in its varied forms, physical and mental, which the body is capable of exerting. Besides these, nitrogen, obtainable from certain vegetable products, not from all, but forming definite combinations with the three elements just named, is essential to the repair and reproduction of the body itself, being one of its most important constituents. Lastly must be named several other elements which, in small proportions, are also essential constituents of the body, such as sulphur, phosphorus, salts of lime, magnesia, potash, etc., with traces of iron and other metals. All these must be present in the food supplied, otherwise animal existence can not be supported; and all are found in the vegetable kingdom, and may be obtained directly therefrom by man in feeding on vegetables alone. But the process of obtaining and combining these simple elements into the more complex forms which constitute the bases of animal tissues—definite compounds of nitrogen with carbon, hydrogen and oxygen—is also accomplished by the lower animals, which are exclusively vegetable feeders. These animals we can consume as food, and thus procure, if we please, ready prepared for our purpose, the materials of flesh, sinew, and bone for immediate use. We obtain also from the animal milk and the egg, already said to be "perfect" foods; and they are so because they contain the nitrogenous compounds referred to, fatty matter abundantly, and the various saline or mineral matters requisite. But compounds simpler in form than the preceding, of a non-nitrogenous kind, that is, of carbon, hydrogen, and oxygen only, are necessary as food for the production of animal heat and force. These consist, first, of the fat of animals of various kinds, and of butter; and from the vegetable kingdom, of the fatty matter which exists in grain and legumes, and largely in the olive and in many seeds; secondly, of the starchy matters, all derived from vegetables, such as a large part of wheaten and other flour, rice, arrowroot, and potatoes, together with sugar, gum, and other minor vegetable products of a similar kind. The fats form the more important group of the two, both in relation to the production of heat and force; and without a constant supply of fat as food the body would cease to exist. The vegetable-eater, pure and simple, can therefore extract from his food all the principles necessary for the growth and support of the body as well as for the production