The popular division of foods into animal and vegetable is neither scientific nor satisfactory. Not that it is a matter of indifference whether man lives on a purely animal or purely vegetable diet or on one derived from both kingdoms, but the differences depend not on the source whence the foods are obtained, but on the proportions in which the various food elements are combined, and on the digestibility and other special properties of the foods selected. The materials supplied in the form of food, and digested and absorbed by the body, are partly employed for building up growing organs and making good the wear and tear—the loss of substances—which they are constantly undergoing, and partly as fuel for the production of heat and of energy. Speaking roughly, raw meat of ordinary quality consists of water seventy-five per cent, albumen and nitrogenous matters twenty per cent, and fat five per cent. Although meat becomes more tender by keeping, it is more wholesome while fresh, and freshness should not be sacrificed for a tenderness really due to the beginning of decomposition. The flesh of mature cattle, that is, four or five years old, is more nutritious than that of younger ones. It is a matter of experience that beef and mutton are more easily digested than veal and pork. Veal broth, however, contains more nutritious matter than mutton broth or beef tea. Poultry and wild birds, if young, yield a tender and digestible meat. Fish vary much in their digestibility, salmon, for instance, being utterly unfit for weak stomachs. Crabs and lobsters are notoriously indigestible. Milk is the sole nourishment provided by nature for the young of man and beast, and contains all food stuffs in the best proportions for the infant’s needs. But milk alone is not adapted to the adult. Supplemented by other food, however, it is invaluable and not appreciated as it ought to be. Cheese is highly nutritious, but not very digestible. Eggs resemble milk in composition, except that they contain less water. The nearer raw the more digestible they are, and the yolk is more so than the white, which, when hard boiled, is the most indigestible form of albumen known. The addition of eggs to baked puddings is of questionable utility, and next to a raw egg, well beaten, in milk or water or in soup or beef tea, not too hot, a light boiled custard is the best form for invalids.