Unfortunately, for the progress of this branch of physiological chemistry, the diet which McCollum had employed successfully for the promotion of growth in young rats was something more than it appeared to be. It was not actually a simple mixture of proteins, several carbohydrates, fats and inorganic salts, but contained as impurities, two nutritive principles which were unsuspected. One of these was in the milk sugar, although this was believed, on the basis of careful tests, to be highly purified lactose; the other was an uncharacterized substance which the butter fat contained. The failure of all investigators in this field to appreciate this led to confusion for several years. The further history of investigations which cleared up this problem will be given in the following chapter.

Fig. 1. - Photograph of A Cow Which Grew Up On A Ration Derived Solely From The Corn Plant. The seed, straw and leaf of the plant were all included in the food mixture. Her nutrition was excellent, as shown by her appearance, the vigor of her offspring and her ability to produce an abundance of milk. Figure 2 shows a photograph of her calf, taken soon after it was born. Rations consisting of the entire plant may be highly satisfactory. The seed of the plant is never in itself a complete food.

Fig. 2. - Photograph of Calf Produced By A Mother Whose Ration Had Been Long Derived From The Corn Plant as the sole source of nutriment. It was vigorous and developed normally. The entire wheat plant, seed, leaf and stem make a diet which can support growth, but not good nutrition. The corn kernel alone does not induce growth.

FIG. 4. - Calf produced by cow shown in Figure 3. It was born prematurely, weighed but little more than half as much as calves normally do at birth, and was dead when born. The importance of the source of the food supply, both for the nutrition of mother and the unborn young, is strikingly illustrated by these animals. (Figures 1 to 4 are from Research Bulletin 17 of the Wisconsin Experiment Station.)