102 HELEN DEAN KING 



7. Individuals in the sixteenth to the twenty-fifth generations 

 of the inbred strain had about the same average body weight at 

 different age periods as had the individuals of the stock controls 

 reared in 1913 to 1915 under favorable conditions of environ- 

 ment and of nutrition (figs. 7 and 8; compare graph B with 

 graph C). Seemingly, therefore, inbreeding has as yet pro- 

 duced no deterioration in the original Albino stock as regards 

 the rate and extent of growth in body weight. 



8. Variability in the body weights of the animals in the later 

 generations of the inbred strain followed the same general trend 

 as that in the animals of the earlier generations and in those of 

 the two stock series studied: in both sexes it increased from birth 

 to sixty days, and then decreased steadily until the animals 

 were about 300 days of age, tending to rise again in older rats 

 (table 12). 



9. In the later generations of the inbred strain the males were 

 more variable in body weight than the females. This result 

 agrees with the finding for the animals of the earher generations 

 and for various series of stock Albinos. 



10. In the inbred animals of the sixteenth to the twenty-fifth 

 generations variability in body weights was relatively high, and 

 it did not tend to decrease with the advance of inbreeding as 

 in the earlier generation (table 13). 



11. Outbred stock Albinos, reared simultaneously with and 

 under the same environmental and nutritive conditions as the 

 inbred rats of the twenty-first to the twenty-fifth generations, 

 showed a variability in their body weights at all ages much 

 greater than that in the animals of the earher stock series reared 

 under more favorable conditions of nutrition. It appears, there- 

 fore, that the increased variabihty in the body weights of the 

 animals in the later generations of the inbred strain was due to 

 the action of environment and of nutrition, not to the effect 

 of continued inbreeding. 



