UNIDENTIFIED VITAMINS 89 



The test animals grew at a suboptimal rate or gained only 1.7 grams/ 

 week. The addition of 2% casein or 0.5% crystalHne trypsinogen to 

 the basal ration caused restoration of the normal growth or a gain of 

 3.1-3.6 grams/week. The addition of a strepogenin concentrate equiva- 

 lent to 2% casein also caused normal growth, but the addition of hydro- 

 lyzed strepogenin concentrate at twice the casein level (4%) had no 

 effect on the suboptimal growth rate (Table XXI). 



These observations and others led to the conclusion that the growth 



TABLE XXI 



Growth Stimulant in Proteins for Animal Nutrition 

 Growth Response of Mice to Certain Proteinaceous Materials 



(Woolley, 1945) 



Average 

 Number change 

 of in weight 



Addition to basal ration % Animals grams/week 



promoting powers of some proteins when added to diets based on amino 

 acids may be attributed to the presence of strepogenin. 



Womack and Rose have described the results of their experiments 

 which indicate that proteins contain an unidentified growth stimulant 

 for rats, which is necessary for the maximum increases in weight and 

 which may be identical to strepogenin. For example, they found that 

 rats on a certain amino acid diet gained about 97 grams in weight in 

 28 days, but when a supplement of 5% casein was added, the average 

 gain was 126 grams. The addition of 5% acid-hydrolyzed casein was 

 considerably less effective in promoting growth (Table XXII). Such 

 experiments indicated that this factor was present in more than seven- 

 teen proteins and protein-rich foods. 



