Relation of Plasticity to Sex and Age. 



65 



habit of choosing a white box instead of a black box was estab- 

 lished by means of systematic training, on the basis of the associa- 

 tion of an electric shock with the latter. Each animal was sub- 

 jected to ten tests daily until it chose correctly on three consecutive 

 days. The habit was then considered perfect and the training 

 ceased. We may speak of the number of tests necessary for the 

 establishment of a perfect habit as the index of plasticity. The 

 index, then, may be defined as the number of tests up to the point 

 at which errors of choice ceased for at least three days. 



In order to discover the relation of sex and age to plasticity 

 five pairs of mice were trained for each of the ages, one, four, and 

 seven months. The investigation is unfinished, as older individuals 

 are to be tested. 



Table : Indices of Plasticity. 



Age. 



Males. 



Females. 



Both. 



I month 



82 



106 



94 



4 months 



128 



106 



II 7 



7 months 



I92 



I46 



169 



In this table each index for the males and the females is the 

 average for five individuals. In the last column the results for the 

 sexes are combined. 



Sex differences which appear in the above table. 



1. At the age of one month the males learn more quickly than 

 do the females. The males require only 82 tests ; the females 

 require 106 for the establishing of a perfect habit. Consequently 

 the index of plasticity for the one-month males is 82 ; that for the 

 one-month females, 106. 



2. At the age of four months the opposite is true. The 

 females learn much more quickly than the males. As the table 

 shows, the index for the males is 128; that for the females 106. 



3. At the age of seven months a similar relation holds. 



Age differences which appear in the above table. 



1. From one month to seven, at least, the plasticity of the male 

 dancer steadily and rapidly decreases. 



2. There is little change in the plasticity of the female dancer 

 between the first and the fourth month. If anything the rapidity 

 of learning tends to increase. Between the fourth and seventh 



