86 HELEN DEAN KING 



during early life, but in the adult state this relation was reversed 

 and the females in the A series were about 2 per cent heavier, 

 as the graphs in figure 6 indicate. 



In the seventh to the fifteenth generations of the inbred strain, 

 also, the animals of the two series had about the same average 

 body weight at corresponding age periods, although, as a group, 

 the individuals of the B series were shghtly heavier (King, '18; 

 tables 11 and 12). Throughout the period of over nine years 

 that this experiment has been in progress, therefore, body growth 

 in the individuals of the one inbred series has closely paralleled 

 that of the individuals in the other series. If the varying con- 

 ditions of environment and of nutrition to which the animals 

 of the inbred strain have been subjected have had any influence 

 on the heritable factors on which growth depends, it is evident 

 that they have acted on the animals of both series in a similar 

 way. I am strongly inclined to the opinion that environmental 

 and nutritive conditions do not influence genetic growth factors 

 directly, but that they act by either stimulating or retarding 

 the growth processes. 



Body-weight data for a total of 606 individuals, 296 males and 

 310 females, belonging in the sixteenth to the twenty-fifth genera- 

 tions of the inbred strain are given in table 10. Reference to 

 this table, which is a combination of the data in table 8 and in 

 table 9, will be made later. 



In connection with another problem I have recently taken a 

 series of body-weight records for a second group of outbred stock 

 Albinos. Supposedly these rats represented the best stock in 

 our colony at the time that the investigation was begun (1916), 

 as care was taken to select for breeding the largest and apparently 

 the most vigorous individuals from the large number available 

 for this purpose. These stock Albinos were reared simultane- 

 ously with, and under the same environmental and nutritive 

 conditions, as the inbred rats of the twenty-first to the twenty- 

 fifth generations. The body-weight data for these animals are 

 given in table 11. 



A comparison of the body-weight data for the stock Albinos 

 (table 11) with that for the inbred group (table 10) shows that 



