LIFE PROCESSES IN CAPTIVE GRAY RATS 15 



Important experimental work during recent years has shown 

 that body growth in rats can be accelerated, and also greatly 

 increased, by feeding nutritional diets or by the use of growth 

 promoting hormones (Robertson, '16 a; Evans, '24; Osborne 

 and Mendel, '26; Mendel and Cannon, '27; Smith and Bing, 

 '28; Anderson and Smith, '32; Mendel and Hubbell, '35, etc.). 

 To what extent other life processes are affected by these 

 agencies has received little attention, as yet. Whether rapid 

 growth during early life is beneficial to the individual and 

 tends to a more active reproductive life and to longevity has 

 long been questioned. Precocious body growth in man has 

 never been deemed advantageous, since it seems to render 

 individuals prone to certain diseases and to shorten the life 

 span. It has been suggested that the difference in the growth 

 rate of the sexes may be responsible for the fact that women 

 tend to live longer than men, even when the latter have not 

 been engaged in hazardous occupations that are liable to 

 shorten life. 



The relation between growth rate and longevity in albino 

 rats has been investigated by McCay and his associates 

 (McCay, '33; McCay and Crowell, '34; McCay, Crowell and 

 Maynard, '35). These investigators found that individuals in 

 which growth was retarded for a number of months by re- 

 stricting the diet still retained the power to grow when they 

 were old if then they were given adequate food. They did 

 not, however, attain the size of animals that had grown 

 rapidly during early life. Individuals with a retarded growth 

 rate lived longer than did the controls, and females had a 

 longer life span than males. McCay ('33) states: "No one 

 has ever found it possible, however, to have both rapid growth 

 with early attainment of maturity and longevity : It is possible 

 that longevity and rapid growth are incompatible and that the 

 best chance for an abnormally long life span belongs to the 

 animal that has grown slowly and attained a late maturity." 



The greater growth acceleration during early life and larger 

 adult size of gray rats in later generations had no apparent 

 detrimental effects on other life processes. On the contrary, 



