334 HUMAN BIOLOGY 



fact that something, which was lacking in his basal diet, was 

 contained in the whey from which the casein and fat had 

 been ehminated. He states: "My intention is only to point 

 out that there is a still unknown substance in milk which even 

 in very small quantities is of paramount importance to 

 nourishment. If this substance is absent the organism loses 

 the power properly to assimilate the well-known principal 

 parts of food, the appetite is lost, and with apparent abundance 

 the animals die of want. Undoubtedly this substance not only 

 occurs in milk but in a series of foodstuffs both of vegetable 

 and animal origin. " 



The following year Hopkins in England described exper- 

 iments almost identical with those of Pekelharing and drew 

 the same deductions. 



After 1900 rapid progress was made in the study of the 

 chemical properties of individual proteins isolated from 

 many foods, and it soon became apparent that proteins 

 are of many kinds, and that they yield varying proportions 

 of their several digestion products. 



Interest was greatly stimulated in the study of nutrition 

 by a series of experiments conducted between the years 1906 

 and 191 1 at the University of Wisconsin. In these experiments 

 animals were fed diets restricted as to source, certain ones 

 being fed solely upon corn products, others upon oat prod- 

 ucts, and still others on wheat products, etc. In the case of 

 cattle, the leaf, stem and seed were all included in the ration, 

 but in the case of mammahan animals, such as farm pigs and 

 rats, diets of a yet simpler character were tested. The curious 

 discovery was made that none of the cereal grains, such as 

 whole wheat, rolled oats, corn meal, either singly or collect- 

 ively were adequate for the support of growth and the promo- 

 tion of well-being in animals when they formed the sole source 

 of nutrient. It was later found that even diets of great 

 complexity, the components of which were derived solely 

 from cereal grains, peas, beans, tubers, starchy roots and 

 fruits, proved insufficient for the promotion of satisfactory 

 growth or for the maintenance of prolonged physiological 

 well-being. At one time a diet containing 23 articles, all 

 known by experience to be wholesome components of 

 the diet, was tested on young rats and found inadequate. 



