50 MILK AND ITS PRODUCTS AS FOODS 



made up of purified milk constituents. McCollum and Davis 

 next tried the wheat seed or kernel. They reasoned that it con- 

 tained protein, carbohydrates and mineral salts and fats or oil, 

 and that if these were mostly equal in quality to those of milk 

 the only foodstuff that might have to be added would be a growth- 

 promoting fat. They first fed wheat alone and then tried the 

 improvement of it with respect to one dietary factor at a time. 

 The following indicates the different combinations in which 

 wheat was fed, with results secured: 



(1) Wheat alone No growth, short life. 



(2) Wheat, plus purified protein No growth, short life. 



(3) Wheat plus a salt mixture which gave it a 



mineral content, similar to that of milk Very little growth t . 



(4) Wheat plus a growth-promoting fat (milk- 



fat) No growth. 



(5) Wheat, plus the protein, plus the salt mix- 



ture Good growth for a time, few or no 



young, short life. 



(6) Wheat, plus protein, plus a growth-pro- 



moting fat (milk-fat) No growth, short life. 



(7) Wheat, plus the salt mixture, plus the 



growth-promoting fat (milk-fat) Fair growth for a time, few or no 



young, short life. 



(8) Wheat, plus protein, plus the salt mixture, 



plus a growth-promoting fat (milk-fat) Good growth, normal number of 



young, good success in rearing 

 young; life approximately the 

 normal span. 



This series of experiments again proves the necessity of a 

 growth-promoting fat. But it does more than this; it shows that 

 the proteins and mineral matter from different sources are not 

 of equal value, those of milk being altogether superior in this 

 respect to those of such a food as wheat. Other experiments 

 proved that the seeds of other cereals are, like wheat, quite 

 incomplete in themselves as diets. 



In following up this investigation it was found that when 

 polished rice was substituted for wheat, in No. 8 of the series of 

 experiments just outlined, the diet failed utterly to induce 

 growth. This was puzzling. The investigators had been able 

 to induce successful growth through feeding a diet composed of 



