BIOLOGICAL CLASSIFICATION OF FOODS 49 



and, as has already been indicated, includes students of the sub- 

 ject extending from America to Europe and even to far-away 

 Japan. Without doubt the best known of these in America is 

 Dr. E. V. McCollum, whose extensive and most valuable articles 

 appeared in Hoard's Dairyman and other farm and scientific 

 journals, and who has issued a valuable book on the subject, 

 entitled, " The Newer Knowledge of Nutrition." In this book 

 he outlines the investigations conducted by him and his co- 

 workers Babcock, Hart, Davis, Steinbeck, Humphrey, Parsons, 

 Funk, Kennedy, Simmonds and Pitz and also familiarizes us 

 with the work of many other investigators. 



As McCollum intimates, in order to secure reliable and exact 

 data it was necessary to feed purified foodstuffs (purified protein, 

 carbohydrates, fats and mineral salts), and in order to do this 

 and secure sufficient data within a reasonable time it was neces- 

 sary to experiment with small animals. For these reasons, 

 the experiments were conducted mostly with young rats, although 

 like results were also obtained with other animals, including 

 cattle and pigs. Accumulated data, from a variety of sources, 

 show that the results secured are equally applicable to the different 

 animals, including man. 



In one of the earlier experiments with rats, conducted by 

 McCollum and Davis, they fed a diet composed of purified pro- 

 tein (casein) to the extent of 18 per cent, lactose or milk-sugar 

 20 per cent (supposed to be pure), about 5 per cent of some fat, 

 together with a salt mixture made up in imitation of the mineral 

 matter of milk, and the balance of starch to make up 100 per cent. 

 The results of this experiment were that when the fat used was 

 milk-fat growth could be secured, but that when this was 

 replaced by such fats as lard, olive oil or other vegetable oils, 

 there was no growth. When the fat of yolk of egg was used 

 instead of milk-fat it also induced growth. These experiments 

 established the fact that fats from different sources are by no 

 means equal in dietary value. 



Following this a more elaborate experiment was planned and 

 carried out by McCollum and Davis. It will be noted that the 

 diet of purified foodstuffs, which proved a satisfactory one, was 



