32 HELEN DEAN KING 



growth of the selected stock males reared as controls for the 

 inbred group. Data in table 13 and in table 14 show that at 13 

 days of age the inbred males weighed, on the average, 1.4 grams 

 more than did the stock males of the same age, but that at thirty 

 days of age the average body weight of the stock group was two 

 grams more than that of the inbreds ; after this age inbred males 

 increased in body weight much more rapidly than did the stock 

 animals. When the rats were at their prime, at eight months 

 of age, inbred males were about 12 per cent heavier than the 

 males of the control series. 



The above analysis of data shows that not only were inbred 

 males of the seventh to the fifteenth generation much heavier 

 than the general run of stock animals at any given age, but that 

 they were also larger, except at the thirty day period, than 

 the selected stock controls reared under similar environmental 

 conditions. 



Graphs showing the weight increase with age for various 

 groups of stock and inbred females are given in figure 12. 



In figure 12 graph A, which indicates the body growth of the 

 females of Donaldson's series of stock albinos, is not strictly 

 comparable to the other graphs, since it was constructed from the 

 actual weight data for unmated females only up to the ninety 

 day period, beyond this point the data used were those of un- 

 mated females corrected to accord with the weights of breeding 

 females as calculated by Watson's ('05) formula: all other 

 graphs were based on the actual weight data of breeding females. 

 Graph A runs lower than either the graph for the inbred females 

 (B) or that for the stock controls (C) during the period in which 

 the actual weight records were used in constructing the graph, 

 but later it is considerably higher than the other graphs. It 

 would seem as if the corrective factor introduced in Watson's 

 formula was much too high, since no series of actual weight 

 records for the albino rat yet reported comes up to the standard 

 required by Donaldson's graph. 



In figure 12 the graph for the growth of inbred females (B) 

 and that for the females in the control series (C) run very close 

 together throughout their entire length. From the thirty to 



