30 



THE AMERICAN NATURALIST 



[Vol. LV 



and inoculation. The birtliweight varies betweW 40 and 

 120 grams, the weight at 33 days b'etween 90 and 360 

 grams, and as to rate of gain after 33 days, some lost 

 weight while others gained over 3 grams a day. 



Age is a factor which must be considered apart from 

 weight and rate of gain. In lots 10-14, there were varia- 





























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tions between 35 and 105 days at the time of inoculation. 

 In lots 7-9 the variation was between 45 and 85 days. 



The correlation between the length of life after inocu- 

 lation and each of these factors, including also size of lit- 

 ter, is given in Table III for lots 7-9 and lots 10-14. All 

 of these correlations were calculated by the usual product 



