A PHYSIOLOGICAL CHARACTER. 109 



quantitative differences in favor of the plus strain averaged greater 

 than those for the minus strain, so that on the whole the plus strain 

 averaged somewhat higher in reproductive vigor. For the first 11 

 periods (23 months) this superiority in vigor in the plus strain was 

 marked; but, during the remainder of the experiment (16 two-month 

 periods) during which the divergence in mean reaction-time became 

 very large, the average superiority of the plus strain in reproductive 

 vigor was slight indeed, and, in fact, during 9 of these 16 periods the 

 minus strain was the more vigorous. This at once throws serious 

 doubt upon the possibility of explaining any portion of the diver- 

 gence in mean reaction-time as a result of a difference in vigor. 



2. Near the middle of the curve for 5 successive two-month 

 periods the minus strain showed (see figure 18, a and b) a slight 

 superiority in reproductive vigor over the plus strain, and during 

 this time the minus curve twice approached the plus curve, although 

 in spite of its greater vigor the minus strain had a consistently 

 higher reaction-time. Examination of the curves at this point might 

 at first sight seem to suggest, however, that there was actually some 

 effect upon mean reaction-time of the relatively greater vigor of 

 the minus strain. At two points the curves covering this limited period 

 are separated by spaces representing differences in reaction-times of 

 only 64 and 20 seconds, but at the other three points the curves are 

 separated by 219, 133, and 101 seconds (table 44). These last three 

 divergences are larger than had occurred except in 3 of the 1 1 preced- 

 ing periods of the experiment. The mean reaction-time for all the 

 data for the plus strain during this ten-month period of superior 

 vigor on the part of the minus strain was 613.7 seconds, 119.2 seconds 

 (19 per cent) less than that for the minus strain, whose reproductive 

 index during this time averaged 0.10 higher than that for the plus 

 strain. This may be compared (a) with similar averages for all 

 data for Line 757 obtained previous to October 1914, during which 

 the mean reaction-times differed by 68.7 seconds (10 per cent), the 

 minus strain having the higher reaction-time and a less vigor by 

 0.25; (b) with the period of 10 months immediately following the 

 ten-month period of superior reproductive ability on the part of the 

 minus strain, in which the plus strain was the superior in vigor by 

 0.19 and its reaction-time averaged 325 seconds (71 per cent) less; 

 and (c) with the final 6 periods (11 months), during which the plus 

 strain had a lower reproductive index by only 0.08 and a lower mean 

 reaction-time by 300.6 seconds (nearly 89 per cent). This shows 

 that the rapidly increasing percentage difference between the mean 

 reaction- times was quite independent of the relative vigor of the two 

 strains. 



Further, in the 2 two-month periods immediately preceding the 

 5 periods of superior vigor on the part of the minus strain just 

 referred to, the minus strain showed a greater reactiveness to light 



