300 CARNEGIE INSTITUTION OF WASHINGTON. 



cent of the zein, is added to the diet, mature animals are maintained 

 for a long time. We have now found that young animals can be 

 maintained for long periods by this diet, but that they fail to grow; 

 and further, that if a similar quantity of lysine is also added to the 

 food, they can grow for a considerable time at a nearly normal rate. 

 If a part of the zein of the food is replaced by another protein capable 

 of promoting normal growth, young animals grow as rapidly, and for 

 as long a time, as if the entire protein of the diet consisted of one 

 adequate for growth. Different proportions of each of the several 

 proteins tested are required to render zein effective for satisfactory 

 growth. A mixture of one part of lactalbumin and four parts of zein 

 promotes growth at a normal rate, but a mixture of equal parts of 

 casein and zein, or one part of zein and three of edestin, is required 

 to produce the same result. 



Differences in the proportions of the amino-acids contained in the 

 molecules of these proteins may account for the widely different 

 quantities of each of them required to supplement the deficiencies of 

 zein. Thus edestin yields a relatively small proportion of lysine, 

 which is wholly absent from zein. On a diet containing equal parts 

 of zein and edestin very little growth is made, but if tryptophane and 

 lysine are each added, in a proportion equal to 3 per cent of the zein, 

 normal growth ensues. It is possible that the superior efficiency of 

 lactalbumin in supplementing zein is due to a high content of both 

 lysine and tryptophane. 



Young rats fed on diets containing either zein or phaseolin, as the 

 sole protein of the diet, decline rapidly in weight, but when given a 

 food containing equal parts of these two proteins they are main- 

 tained, but do not grow. These experiments are of interest in con- 

 nection with the feeding of corn, for they indicate that this important 

 cereal can be utilized most profitably when fed in combination with 

 other foods containing proteins which, by their chemical constitution, 

 best supplement the deficiencies of zein. 



In this connection experiments have been made with a preparation 

 of ''corn gluten," which is a by-product of the manufacture of starch 

 and is largely used as a concentrated feed for domestic animals. 

 This product contains about 31 per cent of zein, 14 per cent of protein 

 insoluble in alcohol, but soluble in dilute alkali, 5 per cent of ether- 

 soluble matter, and about 50 per cent of insoluble carbohydrates, of 

 which a part is starch. Foods were made with this corn gluten in 

 such proportions as to imitate as nearly as possible the proximate 

 composition of our standard "protein-free milk" diets. These con- 

 tained 18 per cent of the corn protein, a quantity of the carbohydrate 

 of the standard food being substituted by the carbohydrate supplied 

 by the corn gluten. On this diet rats have been well maintained for 

 long periods, but with very little growth. Replacing a part of the 



