Different substances are nutritious in proportion as they yield, when digested, those elements which are found to exist in the different tissues of the body. Animals do not possess the power of forming new elements, or of converting one element into another, and it necessarily follows that the elements of their growth and nutrition must be derived from the food which they take. The largest part of nearly all the substances which make up the human body are composed of oxygen, hydrogen, nitrogen and carbon, and different substances are regarded as nutritious in proportion as they furnish these essential elements of our organization. In general, those substances may be regarded as the most important articles of diet which furnish, with the greatest facility of digestion, the largest amount of these elements. Milk is regarded, perhaps correctly, as the plainest and simplest kind of food. Cow’s milk is composed of: Casein, 4.48 Butter, 3.13 Sugar of milk, 4.77 Various salts, .60 Water, 87.00 Milk, being furnished by nature as the only food for the young of the mammalia during a certain period of their existence, contains all the elements necessary to the nutrition and the growth of the body. Out of the casein are formed the albumen and fibrin of the blood. The butter serves for the formation of fat, and contributes, with the sugar, to the support of animal heat, by yielding carbon and hydrogen to be burnt in the lungs. The earthy salts (phosphate of lime, etc.) are necessary for the development of the bones, the iron required for the blood, corpuscles and the hair. In this country, meat constitutes an important part of the diet of almost every family. As a general rule, animal food is more easily digested, contains a greater amount of nutriment, and is more stimulating than any of the varieties of vegetable food. As minuteness of division and tenderness of fibre facilitate digestion, young meats are more tender than old; thus, roasted pig is more speedily digested than broiled pork; steak and boiled lamb sooner than boiled mutton. Still, there are some exceptions to the digestibility of young meats, veal, and with some persons lamb, are slower of digestion than beef or mutton.