82 HELEN DEAN KING 



life (figures 7 and 8, graph B), but this was undoubtedly due 

 to the action of environmental and nutritive conditions, not to 

 inbreeding. Any agency influencing growth, whether it be bene- 

 ficial or detrimental, naturally produces its greatest effect during 

 the period when growth is normally most rapid and vigorous. 

 Since unfavorable conditions of environment and of nutrition 

 unquestionably limited the extent of body growth in the animals 

 of the later generations of the inbred strain, it is very probable 

 that these factors also lessened the rate of growth durmg the 

 early life of the individuals. If body growth in the inbred rats 

 of future generations is retarded during the adolescent period, 

 although the environmental and nutritive conditions under which 

 the animals live are such that they produce rapid and vigorous 

 growth in outbred stock Albinos, the change in the rate of growth 

 can be ascribed to the effects of inbreeding. As far as the ex- 

 periment has gone at present, the evidence does not warrant the 

 conclusion that inbreeding per se has altered the form of the 

 growth graph to any appreciable extent. 



The body-weight data for the animals in various generation 

 groups of the two inbred series, as given in table 5 and in table 

 6, were combined in order to show the weight increase with age 

 in the individuals of the inbred strain as a whole. The combined 

 data are shown in table 7. 



The data in table 7 are not presented graphically, since there 

 was such a close agreement between the corresponding records 

 for the various generation groups of the two series that graphs 

 constructed from the combined data would not differ materially 

 from those given for the separate series (figs. 1 to 4). 



Table 8 gives data showing the increase in the weight of the 

 body with age for all of the individuals in the sixteenth to the 

 twenty-fifth generations of the A series of inbreds for which 

 growth records were taken; table 9 shows similar data for in- 

 dividuals of the B series. 



A comparison of the data in table 8 with corresponding data 

 in table 9 shows that the rats in the two inbred series were much 

 alike as regards the rate and extent of their growth in body 

 weight. To show this similarity more clearly, weight data for 

 the males of the two series are presented graphically in figure 5. 



