A PHYSIOLOGICAL CHARACTER. 41 



descent, i. e., if mothers of the same generation of descent in the 

 two strains produce their young on the same day the circle will fall 

 upon the base-line with the figure adjoining. If young from the 

 same generation of descent appeared 13 days later in the plus than 

 in the minus strain, the solid circle will fall on the base-line with 

 a figure 13 placed above the line, while if the minus strain (as in the 

 case of the seventh entry in this diagram) were 4 generations and a 

 day behind the plus strain in producing young of a given generation, 

 this is indicated by the open circle being placed 4 units below the 

 base-line, with a figure 1 adjoining. 



By comparing the relative amounts of descent of the two strains 

 from the end of one two-month period to the end of the following 

 two-month period, one can determine whether the plus or the minus 

 strain had during that interval descended the more rapidly, i. e., 

 which strain was presumably the more vigorous of the two during 

 that limited period. For example, from the end of May 1912 (first 

 entry in this diagram) to the end of July 1912 (second two-month 

 period and second en^ry in the diagram), the minus strain from 

 having been 1 generation and 2 days in advance of the plus strain 

 had become 13 days ahead of the plus strain in its time of producing 

 young of the same generation of descent. During the following two- 

 month period (the third) the minus strain became just 1 generation 

 (third entry in the diagram) behind the plus strain. Still one period 

 later (the fourth) it was 1 generation and 7 days in arrears of the 

 plus strain. 



Comparing rate of descent with mean reaction-time, the minus 

 strain during the second two-month period descended the less rapidly, 

 but was the more reactive of the two strains. During the third 

 period the minus strain descended the less of the two strains and was 

 the less reactive. During the fourth period the minus strain again 

 descended the less rapidly and was the less reactive. While the 

 difference in reaction-time is frequently in the direction expected if 

 influenced or determined by the relative rates of descent of the two 

 strains, such is not true more often than the reverse is true. For 

 the 27 two-month periods of selection with Line 695, the more 

 rapidly descending of the two strains had the lower reaction-time 

 in 10 cases, the higher reaction-time in 13 cases; for 3 two-month 

 periods their rates of descent were identical; and for 1 period their 

 mean reaction-times were identical. That is, the more vigorous 

 strain, judged by its rate of descent, was the less reactive during 13 

 of the two-month periods, and in fewer cases (10) the more vigorous 

 strain was the more reactive one. Hence, judged by this measure 

 alone, the more vigorous strain was the more reactive strain less 

 often than it was the less reactive strain. 



In a further endeavor to learn if relative vigor is a factor in 

 influencing reaction-times, all of our data for Line 695 which seemed 



