JANUABT 31, 1913] 



SCIENCE 



187 



zein food efficient for maintenance over a long 

 period. 



Our experiments show that there is a very 

 great difference in the food value of different 

 proteins. Thus we have complete nutritive 

 failure with zein, maintenance with gliadin, 

 and restoration of lost weight, or normal 

 growth, with either casein, lactalbumin or 



which is still in progress, indicates that the 

 failure to grow, shown by rat 393, or by rats 

 fed with gliadin, is not due to a lack of lysine 

 in the protein. The fall in weight shown by 

 these two rats at tlie beginning of the experi- 

 ment is probably chiefly due to the less bulky 

 experimental food, and the consequent smaller 

 quantity of feces in the digestive tract. 



a)As|E 



l^A-is 



Chart II 



edestin. These three latter proteins yield on 

 hydrolysis both tryptophane and lysine, which 

 zem lacks, whereas bliadin, which is incapable 

 of promoting growth, yields tryptophane, but 

 only a very insignificant proportion of lysine. 

 Gliadin resembles zein in the proportion of 

 amino-acids, other than tryptophane, but dif- 

 fers widely fi'om casein, lactalbumin or 

 edestin. 



Chart II. shows that when a quantity of 

 tryptophane corresponding to 3 per cent, of 

 the protein is added to the zein food, the rat 

 does not decline in weight, but is maintained 

 without growth, just as if fed with gliadin. 

 The curve for rat 892 likewise shows main- 

 tenance without growth. This experiment, 



Charts I. and II. show that zein is incapable 

 of maintaining rats, unless tryptophane is 

 added to the diet, whereas on the other pro- 

 teins, aU of which yield tryptophane, they re- 

 cover their lost weight, and grow at a normal 

 rate except on gliadin. This raises the ques- 

 tion whether or not the replacement of a 

 part of the zein by other proteins containing 

 tryptophane will render the ration effective in 

 promoting growth. Unfortunately there is no 

 method known whereby the amount of trypto- 

 phane in a protein can be even approximately 

 determined. The nearest approach to an esti- 

 mate of the relative amount is given by a com- 

 parison of the intensity of the color shown by 

 the glyoxylic acid reaction. Such a compari- 



