108 



INBEEEDING AND OUTBREEDING 



curve A 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 



body weight. Albino Rat 

 Males 



20 40 60 80 100 120 140 160 160 200 220 240 260 260 300 320 340 360 380 400 420 440 460 480 



FIG. 26. Graphs showing the increase in the weight of the body 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.igraph. 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 in fertility as is evident if one plots the theoreti- 

 cal curve which fits the experimental curve for litter size 



