544 



THE AMERICAN NATURALIST [Vol. LV 



A second feature of their results, which is no less note- 

 worthy than the first, is the rapidity of growth after 

 adequate diets were given. They show that the gains 

 made by the rats whose growth had been previously sup- 

 pressed were made in much loss time than would be re- 

 quired for a rat on adequate diet to make the same gain 

 in w^eight.*^ This inquiry is concerned only with certain 

 characteristics of the rate of growth following the initial 

 period of suppression and will not attempt any discussion 

 of the nutritional aspects of the problem. The data dis- 

 cussed have been drawn from the w^ork of Osborne and 

 Mendel. It has not been possible to obtain records of 

 enough individuals to give a statistically reliable aver- 

 age, yet the records employed are fortunately free from 

 extreme fluctuations and are satisfactory as far as in- 

 dividual records can go.'^ 



The first case to be discussed is that of a male rat 

 (No. 1012) which at age 370 days had reached a body 

 Aveight of 127 grams, having been fed alternately gel- 

 atin food ' ' and ' ' milk food. " ^ On the 368th day the ra- 

 tion was permanently changed to milk food plus mixed 

 food." This change in diet was promptly followed by 

 rapid growth and the attainment of mature weight about 

 ]80 days later. It is evident from Osborne and Mendel's 

 chart that the curve of " resumed growth " was steeper 

 than the normal curve of growth. This difference is 

 especially well marked during that portion of the time 

 in which there is an actual increase in body size and less 

 well marked during the time in which its increase is due 

 to the formation and deposition of fat. 



A quantitative study of the resumed growth of this 

 animal sh()\\- lli.- exi-trncc (it* two distinct cycles, each 

 of which i^ e\pr.'.^<Ml }.> ail <-,iU;ni..n of the type already 



O^hor.ic, T \I.„,1..| L i; , J „M , /,,,„•. !-hiis«>l. . iO: 16-20,1916. 



