The failure of Slonaker's rats to thrive on the vegetarian diet is to be explained on the basis of several faults. In the first place, the diet was of such a nature that the animals could hardly do otherwise than take a rather low protein intake. Secondly, the leaves, which formed the only components of the food supply containing enough mineral elements to support growth, were fed in the fresh condition. In this form the water content and bulk are so great that it would be practically impossible for an animal whose digestive apparatus is no more capacious than that of an omnivorous rat to eat a sufficient amount of leaf to correct the inorganic deficiencies of the rest of the mixture, which consisted of grains, seeds, tubers, and root foods. The same physical limitations would likewise determine the failure of the animals to secure enough of the fat-soluble A to supplement the deficiency of all the ingredients of their diet other than the leaves. This would not form so important a fault as the inorganic deficiencies but would be an important depressing factor. Success or failure would also turn in great measure upon the extent to which the animals would be guided by instinct in the selection of the proportions of the several types of food-stuffs offered them. In the opinion of McCollum the appetite is by no means so safe a guide for the proper selection of foods as has generally been supposed.

From the results of the experiments just described it was necessary to conclude that the leaf differs from the seed in the respect that it contains in satisfactory amounts the dietary factors found in the latter in too small amounts. (Compare Charts 7 and 8.) These include the three inorganic elements, calcium, sodium and chlorin, fat-soluble A and proteins which supplement at least in some degree those of the seed. These, it will be remembered, are the three and only purified food factors which need be added to each of the seeds in order to make for dietetic completeness. It is, therefore, possible to devise a diet derived entirely from vegetable materials, which will produce normal growth and optimum physiological well-being.

A point of special interest which it is well to emphasize, is that the bones of these vegetarian rats were of very good quality. There was no evidence in any of the young of the occurrence of rickets, a disease which invariably shows a tendency to develop in young animals restricted to a diet of cereal grains. The exact nature of the defects in the diet which causes this disease of the skeleton cannot be profitably entered into here, but will be cone their observations that many women while nursing infants take for days or weeks, diets derived in great measure from tea, toast, sugar and other articles of food equally unfit for the elaboration of milk. The nursing mother should always have a diet of a quality calculated to insure a satisfactory composition of the milk which she is to secrete. This she can best realize by including in her menus liberal amounts of milk and of salads. It is not enough for the diet to yield a proper calorific value, fur-nish protein according to the long accepted standards, and afford variety and palatability. The specific dietary properties of the food mixtures which enter into the diet are of paramount importance and must be given due and weighty consideration.

Chart 10. - The two curves in this chart serve to illustrate the remarkable superiority of whole milk as a supplement to a mixture of cereal grains, legume, seeds, tubers, and fleshy roots as compared with round steak, a muscle meat. Lot 2147 had a complex vegetable diet of the type described, supplemented with a liberal amount (10%) of beefsteak. Their growth was slow and the animals never reached the full adult size. They also developed early in life the appearance of old age. Lot 2148 had essentially the same diet but supplemented with ten per cent of whole milk powder. This served as a source of mineral salts and of fat-soluble A, in which diet 2147 was deficient, and made possible much more rapid growth, larger final size and much longer life. These curves illustrate the importance of the proper selection of food, so as to be highly satisfactory, rather than the adherence to a diet which is somewhat faulty in one or more respects.