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HELEN DEAN KING 



to those of the preceding generations, as graph C and graph D 

 in figure 1 show. Since the number of weighed individuals in 

 a single generation was comparatively small, it is not surprising 

 that the course of graph D should be rather erratic. At its 

 beginning this graph runs very slightly higher than graph C, 

 but at the 90-day period it begins to rise rapidly, and at 334 

 days it crosses graph B and subsequently runs above it until 

 the final weighing. In the A series of inbreds the males of the 



, Fig. 2 Graphs showing the increase in the weight of the body with age for 

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

 (data in table 5; lettering as in fig. 1). 



twenty-fifth generation were, as a group, superior in body weight 

 to the males of the generation preceding. The superiority of 

 these individuals can be attributed in part to an improvement 

 in the nutritive conditions and in part to the fact that the ma- 

 jority of animals in this generation were born at the time of 

 year that experience has shown is most favorable for body growth 

 in the rat, i.e., the winter months. 



Graphs showing the growth in body weight of females belong- 

 ing to various generation groups of the A series of inbreds are 



