This is the most satisfactory single article of food which is suitable for consumption by man. It is not an ideal food when taken over a long period as the sole source of nutriment, but is the best one with which nature has provided us. It is the one food for which there is no effective substitute.

Milk is a very effective food for supplementing the deficiencies of other substances such as the cereal grains, tubers and fleshy roots (48). It is rich in both calcium and phosphorus, and many vegetable foods are relatively poor in both these elements, especially the former. In fact, there are but two classes of foods which are relatively rich in calcium, the principal element in lime, and a prominent constituent of the substance of bone. These are the milks of various animals and the leafy vegetables. All other kinds of foods fall below the nutritive requirements of man and animals in this substance. The body is very sensitive to deviations from the optimal concentration of calcium in the food, and serious damage may easily result to the bone structures if the diet is not properly constituted with respect to this substance.