It has been shown what chemical constituents form a satisfactory diet for a mammal and the experimental evidence upon which the accepted views rest has been described.

The dietary properties of each of our more important agricultural products and of each of the animal products serving as food for man have been pointed out. Emphasis has been laid upon the manner and extent to which foods which are, individually deficient in one or more respects tend, when combined, to correct each other's deficiencies. The evidence is overwhelming that the keynote to successful nutrition is the selection of foods having unlike dietary properties, but so constituted as to supplement each other's deficiencies and to make a mixture which affords the most satisfactory amounts of each of the essential food elements, rightly combined. The generalization has been made that a diet may afford a surprisingly great variety of food-stuffs, including cereal grains, tubers, fleshy roots, fruits, and liberal additions of muscle meats, and still fall far short of being adequate for the support of growth or for the maintenance of health in the adult. In the present chapter, the types of diets which are successful in a rather high degree will be described, and their effects on man and animals will be illustrated. At the same time the errors in the selection of food which mark the habits of a number of groups of people in different parts of the world, will be pointed out.