Death ensues if salts are withheld from the food. They are essential for the growth and repair of the tissue. There are no exact data available for indicating how much is required, but we know from experience that there is enough in an ordinary mixed diet, the mineral matter being present, as a rule, in organic combination. Calcium is specially required for the growth of bone - it occurs abundantly in milk, eggs, and rice; meat foods are deficient in calcium. Oxalate of lime is present in certain foods, notably tea, coffee, spinach, rhubarb, and pepper. It is absent in animal foods. About 10 milligrams of iron are required daily, and are taken inorganic combination. It is relatively abundant in meat and yolk of eggs; it is deficient in milk and its derivatives. For this reason, persons who are kept for a long time on a purely milk diet are apt to become anaemic. It might be assumed that the paucity of iron in milk is a disadvantage in the feeding of infants and young children, but this is not so, as the young child has a large reserve store of iron in the liver which it has obtained from the blood of the mother.

Vegetable foods, e.q:, green vegetables and fruits, are rich in potassium; animal foods are rich in sodium. It is probable that the potassium in vegetables and fruits acts beneficially, largely because of the vegetable acids with which it is combined, and which by oxidation assists in maintaining the normal alkalinity of the blood. Sodium is taken abundantly in the form of common salt, of which about 20 grammes are taken daily in a mixed diet, this amount being considerably above the actual body requirements. Phosphorus is one of the most important mineral ingredients in the food, more especially for growing subjects. It is present in organic form, and also in an inorganic form as phosphates of the alkalis or earthy metals, and there is reason to believe that the former are the more valuable. Animal foods are much richer in phosphorus than vegetable foods. The foods richest in phosphorus in combined organic form, are fish roe, thymus, calves' brains, and the germ of wheat.