98 HELEN DEAN KING 



strain have shown a variability in body weights considerably 

 greater than that found in any group of inbred animals since the 

 tenth generation. 



By comparing the corresponding coefhcents for the two series 

 of outbred stock Albinos that were reared in the colony on differ- 

 ent diets, one can determine whether the variability in the body 

 weights of these animals was influenced by the nutritive con- 

 ditions under which they lived. By a further comparison of these 

 coefficients with those for the animals in the later generations 

 of the inbred strain, it will be possible to determine whether the 

 increase in the variability of the inbred animals was due to al- 

 tered conditions of nutrition or to the effects of long-continued 

 inbreeding. 



All of the stock Albinos reared in 1913 to 1915 as controls 

 for the inbred series were fed on 'scrap' food. As has already 

 been recorded (King, '15; table 4), the coefficients of variability 

 for the body weights of the fifty males in this series range from 

 10.2 to 17.0, with an average of 13.6 for the entire group, taking 

 all ages together; coefficients for the fifty females vary from 

 8.9 to 15.7, with an average of 11.5 for the entire group. 



The second series of stock controls was reared in 1916 to 1918 

 simultaneously with the inbred rats of the twenty-first to the 

 twenty-fifth generations, and they, as the inbred rats, were fed 

 on various experimental diets. These stock Albinos came from 

 the same general stock colony that furnished animals for the 

 first series of controls, so the coefficients for the two series are 

 strictly comparable. An examination of the coefficients for the 

 body weights of the rats in this control series, as given in table 

 1 1 of the present paper, shows that all of them are much larger 

 than the corresponding coefficients for the animals of the first 

 stock series, while the difference between the average coefficients 

 for the two series is over four times the probable error. It is 

 evident, therefore, that the rats in the second series of stock 

 controls were much more variable in their body weights at all 

 age periods than were the animals in the first stock series. Since 

 both of these stock series were outbred, the increased variabihty 

 in the animals of the second series cannot be attributed to the 



