About 200 grains of common salt are required daily by an adult, but a large proportion of this is in our food. Phosphate of lime is obtained from milk and meats, and carbonate of lime from the hard water we drink. Both are required for the bones and teeth. The salts of potash, which assist in purifying the blood, are obtained from vegetables and fruits. An iron salt is found in most foods, and sulphur in the yolk of eggs. 106. Water. Water is of use chiefly as a solvent, and while not strictly a food, is necessary to life. It enters into the construction of every tissue and is constantly being removed from the body by every channel of waste[17]. As a solvent water aids digestion, and as it forms about 80 per cent of the blood, it serves as a carrier of nutrient material to all the tissues of the body. Important Articles of Diet. 107. Milk. The value of milk as a food cannot be overestimated. It affords nourishment in a very simple, convenient, and perfect form. It is the sole food provided for the young of all animals which nourish their young. It is an ideal food containing, in excellent proportions, all the four elements necessary for growth and health in earlier youth. Composition of Food Materials. Careful analyses have been made of the different articles of food, mostly of the raw, or uncooked foods. As might be expected, the analyses on record differ more or less in the percentages assigned to the various constituents, but the following table will give a fair idea of the fundamental nutritive value of the more common foods: In 100 parts Water Proteid Fat Carbohydrate Ash Digestible Cellulose Meat 76.7 20.8 1.5 0.3 — 1.3 Eggs 73.7 12.6 12.1 — — 1.1 Cheese 36-60 25-33 7-30 3-7 — 3.4 Cow’s Milk 87.7 3.4 3.2 4.8 — 0.7 Wheat Flour 13.3 10.2 0.9 74.8 0.3 0.5 Wheat Bread 35.6 7.1 0.2 55.5 0.3 1.1 Rye Flour 13.7 11.5 2.1 69.7 1.6 1.4 Rye bread 42.3 6.1 0.4 49.2 0.5 1.5 Rice 13.1 7.0 0.9 77.4 0.6 1.0 Corn 13.1 9.9 4.6 68.4 2.5 1.5 Macaroni 10.1 9.0 0.3 79.0 0.3 0.5 Peas and Beans 12-15 23-26 1½-2 49-54 4.7 2-3 Potatoes 75.5 2.0 0.2 20.6 0.7 1.0 Carrots 87.1 1.0 0.2 9.3 1.4 0.9 Cabbage 90 2.3 0.5 4-6 1-2 1.3 Fruit 84 0.5 — 10 4 0.5 Cheese is the nitrogenous part of milk, which has been coagulated by the use of rennet. The curd is then carefully dried, salted, and pressed. Cheese is sometimes difficult of digestion, as on account of its solid form it is not easily acted upon by the digestive fluids.