FOOD COMPOSED OF SIMPLE SUBSTANCES 497 



existence. With favorable hygienic conditions and careful 

 attention made possible in the study by the assistance of the 

 Carnegie Institution, they succeeded in keeping rats on arti- 

 ficial diet for a great part of their lives. A diet of the type 

 in mind was made up of a mixture of milk powder, starch, 

 pork fat and salts. If milk was freed of its proteins, and the 

 remainder concentrated, it proved to be a suitable supple- 

 ment for different forms of protein diet, to such a degree 

 in fact that, even when they fed isolated proteins, marked 

 growth of young animals was induced. By this method the 

 possibility of making comparisons between different proteins 

 was afforded. Casein, lactalbumin, crystallized eggalbumin 

 and edestin, and the glutein from wheat and glycinin from 

 the soya bean proved to be of full value. Gliadin (from 

 wheat) and hordein (from barley) , in the catabolism of which 

 glycocoll and lysin enter but little, proved to at least have 

 the power of keeping the bodies of the rats in statu quo, 

 although without growth ; and zein, the tryptophan-, lysin- 

 and gly co coll-free protein of maize, as also gelatine, were 

 found insufficient even for this last purpose. It was repeat- 

 edly noted that proteins devoid of the cyclical molecules of 

 tyrosin and tryptophane were apparently not suitable for 

 satisfying the requirements of growth. With this in mind 

 Osborne suggested the hypothesis that " cyclopoiesis" (that 

 is, ability to build up certain cyclical molecules) is a char- 

 acteristic of the vegetable cell, and that for this reason the 

 animal body may be supposed to be dependent for certain 

 types of its nutriment upon vegetable life. 



Investigations along similar lines have very recently been 

 made in Cambridge by Hopkins : Bats were fed in parallel 

 experiments on mixtures of casein, fat, carbohydrates and 

 salt, with and without addition of a minimal quantity of fresh 

 milk. Although this last addendum formed scarcely four 

 per cent, of the total food in its dried state, it made possible 

 a normal and continued growth ; while the rats fed on the 



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