252 



Morris Rockstein 



longevities from 927 to 1,306 days). Female longevities, on the 

 contrary, were relatively unaffected by such alterations in 

 diet. It would appear from their results that retardation of 

 growth in the male rat by such a dietary restriction eliminates 

 the sex differential in longevity, normally favouring the 

 female rat. However, McCay emphasized the low calorie 

 aspect of his restricted diet, which was in reality a high 

 protein, salt and vitamin diet. It is therefore likely that the 



Table I 



Effect of diet on longevity of male 

 and female house flies 



critical factor involved in such a restricted diet might well have 

 been the effective protein content of the diet. Indeed, the 

 ingestion of such a "low calorie" diet might mean the utiliza- 

 tion of the protein in this diet to meet the basal energy 

 requirements (in the absence of carbohydrates and fats 

 customarily utilized by the body in energizing processes). 

 There would result an unavailability of protein required for 

 normal cell growth, replacement and addition and, therefore, 

 retardation of normal body growth and maturation. This (and 

 evidence to follow) suggests that there may exist for each 

 species a specific protein-calorie optimum for normal growth 



