lUOLOCilCAL CLASSIFICATIOX OF FOODS 49 



anri, as has alrearh' Ijccn iiidicatcil. inclmles students of the sub- 

 ject extendintr Irdin America to Eurnpe and e\en to far-a\\a\' 

 Japan. Without doubt tlie best known (jf these in America is 

 Dr. E. A'. ]McCollum. who.^e exten.-.i\-e and most \"aluable articles 

 appeared in Hoard's lJair\anan and (itlrer farm and scientitic 

 j(jurnals. and who has issued a valuable book on the subject, 

 entitled, " The Xewer Knowledge of Xutrition." In this book 

 he outlines the investi.gations conducterl b}" him and his co- 

 workers — Babcock, Hart. Da\-is, Steinbeck, Humpohre}', Parsons, 

 Funk, Kenned}', Sinimonds and Pitz —and also familiarizes us 

 with the work of man\- other in\-estigators. 



As [NlcC'ollum intimates, in order to secure reliable and exact 

 data it was necessar\' to feed puritied foodstuffs (purified protein, 

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

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

 sary to experiment with small animals. For these reasons, 

 the experiments were conducted mosth' with \"oung rats, although 

 like results were also obtained with other animals, inclucling 

 cattle and pigs. Acciimulalcd data. Jrom a variety ot sources, 

 sho-K' thai the results secured arc cqv.ally applicable to the dijjerent 

 animals, including man. 



In one of the earher experiments with rats, conducted by 

 McCollum and Da\'is, the\- fed a diet composed of purified pro- 

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

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

 together with a salt niLxture 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, oliye oil or other vegetable oils, 

 there was no growth. \\'hen the fat of }-olk 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 b}' [NlcCoUum and Davis. It will be noted that the 

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



