NUTRITION. 301 



corn gluten protein with lactalbuniin, casein, or edestin gave results 

 very similar to those obtained by corresponding additions of these 

 proteins to pure zein diets. The proportion of lactalbumin required 

 to promote normal growth was as small as in the zein experiments, 

 and the superiority of casein over edestin was likewise manifest. 

 These results are in harmony with practical experience in feeding, 

 for a combination of corn meal and milk has long been esteemed as 

 a food for young animals. 



The outcome of these experiments has an important experimental 

 bearing; for foods made with corn gluten have proved unusually 

 effective in maintaining animals at nearly constant weight and in 

 good condition over long periods. By means of this food it will be 

 possible to obtain a large number of stunted animals, for studying the 

 histological changes that occur when growth is suppressed by a diet 

 containing an inadequate protein, as well as for learning the influence of 

 delayed growth on the retention of the capacity to grow and the length 

 of life of animals thus stunted. Furthermore, since large quantities 

 of this corn gluten can be obtained at small cost, similar experiments 

 can now be tried on other species of animals larger than rats. 



The experiments with zein foods to which tryptophane and lysine 

 are added shed new light on the relations of the individual amino- 

 acids to nutrition. While proteins yielding tryptophane are essen- 

 tial for the maintenance of either mature or young animals, those 

 containing lysine also are required for growth. This conclusion is 

 further supported by the fact that, whereas a mature animal can be 

 indefinitely maintained, and even produce young, on a food contain- 

 ing gliadin as its sole protein, a young animal can not grow thereon, 

 unless lysine — in our experiments equivalent to 3 per cent of the 

 protein — is added to the food. These observations appear to be the 

 best evidence yet recorded that the amino-acid complexes are the units 

 with which young animals deal in the construction of new tissue. 



The practical importance of a recognition of this fact is well illus- 

 trated by the recent experiments of Dr. Sweet and his associates, who 

 have succeeded in controlling the growth of tumors, transplanted 

 into mice, by feeding them on one of the diets (described in an earlier 

 paper b}^ us) which was incapable of promoting the growth of young 

 rats. 



During the past year a series of young rats has been carried at 

 nearly constant weight for the purpose of learning how long animals 

 thus stunted can be kept in good physical condition, what is the best 

 way to accomplish this, how long such animals retain the capacity to 

 grow, and what effect suppression of early growth may have on their 

 subsequent development and length of life. These experiments, 

 which have now been in progress for nearly a year, have been so suc- 

 cessful that up to the present time only three of these animals have 



