278 SCIENCE REMAKING THE WORLD 



set forth in our basal principles for food selection and 

 that the failure of animals fed upon purified food mix- 

 tures such as those used by Hopkins and Osborne and 

 Mendel is due to lack of palatability and consequent 

 failure of the animals to eat enough. McCollum's food 

 mixture was made up of the proteins edestin from hemp 

 seed and zein from corn. With these were given corn- 

 starch, wheat starch, milk sugar, glucose, cane sugar, 

 butter fat, bacon fat, and cholesterol and a salt mixture. 

 The striking result was normal growth. In 1909, 

 Osborne and Mendel began their work to evaluate the 

 importance of the protein components of the diet. In- 

 stead of duplicating the diet of McCollum they substi- 

 tuted a simple mixture consisting of milk-casein, starch, 

 lard, and a salt mixture recommended by Rohmann. 

 These animals, unlike McCollum's, failed to grow and 

 by carefully measuring the food intake it was proved 

 that this failure was not due to lack of appetite. At 

 that time no one was able to see any important chemical 

 difference between the two diets. But by substituting 

 for 28 per cent, of the diet the milk residue which they 

 called protein-free milk, they obtained growth. 



It would take too long to follow out all the lines of 

 this experimentation. Out of it came the important 

 information which has brought us recognition of the 

 differences in protein quality. But from the vitamin 

 viewpoint it was still more important. As a result of 

 McCollum's study of his own diet he finally demon- 

 strated the presence of a hitherto unsuspected factor in 

 his butter fat that is absent in lard. He also found that 

 egg yolk contained this substance. At the time of thia 



