108 INBREEDING AND OUTBEEEDING 



curve ^ if it really represented their true body weight. 

 How favorably these inbred strains compare with stock 

 animals is shown in Fig. 26. 



Paralleling the results obtained for body weight were 



d 20 40 00 80 ioO \ZD 140 160 ISO 200 220 .240 260 280 300 320 340 360 380 400 420 440 460' 480 



Fig. 26. — Graphs"" showing the increase in the weight of the bodyf'with age for 

 different series of male albino rats. A, graph constructed from Donaldson's data for stock 

 albinos; B, graph for males belonging in the seventh to the fifteenth generations of the 

 two series of inbreds combined; C, graph constructed from data for a selected series of 

 stock albinos used as controls for the inbred strain; D/graph for males belonging in;. the 

 first six generations of the two series combined. (After King.) 



those upon fertility and constitutional vigor as judged by 

 longevity. Neither was reduced by inbreeding; in fact, 

 there seems to be no doubt but that there was a significant 

 increase in both cases. There was a slight but definite 

 increase la fertility as is evident if one plots the theoreti- 

 cal curve which fits the experimental curve for litter size 



