EFFECTS OF INBREEDING ON BODY WEIGHT 



81 



state their growth was much more vigorous, and their body 

 weights, especially those of the males, compare favorably with 

 the weights of the animals in the group comprising the rats of 

 the sixteenth to the eighteenth generations (graph A) . 



An examination of figures 1 to 4 brings out one fact of con- 

 siderable interest: all of the graphs have the same general form, 

 although they vary somewhat in height. As the form of these 

 graphs is practically the same as that of the growth graphs for 



20 40 60 80 100 120 140 16Q 180 200 220 240 260 280 300 320 340 360 380 400 420 440 



Fig. 4 Graphs showing the increase in the weight of the body with age for 

 females belonging to various generation groups of the B series of inbred rats 

 (data in table 6; lettering as in fig. 1). 



stock Albinos as determined by Donaldson ('06) and others, 

 it follows that close inbreeding, continued through many genera- 

 tions, does not alter the character of the growth graph for the 

 albino rat. Theoretically, it might be expected, perhaps, that 

 long-continued inbreeding would cause a slowing up of the growth 

 processes, since the animals totally lack the stimulus to growth 

 that a condition of heterozygosis seems to give in many cases 

 (East and Hayes, '12; Jones, '18). The body weights of the 

 animals in the sixteenth to the twenty-fifth generations of the 

 inbred strain tended to lag somewhat during early postnatal 



