CROSS-El) UCA TION. 



;89 



CROSS-EDUCATION. 



By E. W. scripture, 



director of the psychological laboratory, yale fxiversity. 



SOME years ago I made the following simple experiment: I 

 arranged a rubber bulb, like that used for releasing a pbo- 

 tograpber's shutter, to connect with a bottle, from which rose a 

 long, vertical glass tube. The bottle contained mercury, and the 

 long tube reached nearly to the bottom. Every part was air-tight, 

 so that when anybody squeezed the bulb the mercury was forced 

 up the vertical tube. It was what is known as a mercury-dyna- 

 mometer. 



During experiments with this dynamometer, what was more 

 natural than to think of trying what would happen if one hand 

 were practiced daily in squeezing the bulb? So one of our gradu- 

 ate students. Miss E. M. Brown, was set to work in the following 

 manner: On the first day she squeezed the bulb as hard as possible 

 with the left hand, while an assistant noted the height of the mer- 

 cury; this was repeated ten times, and the results were averaged. 

 Immediately thereafter she took ten records Avith the right hand. 

 Then, on the following days, with some intermissions, she prac- 

 ticed the right hand by squeezing ten times on each occasion. On 

 the last day she again tested the left hand, which had not been 

 practiced in the meantime. The records ran as follows: 



Thus the left hand had gained about fifty per cent in strength 

 through practice of the right hand. This peculiar phenomenon 

 of transference of the effects of practice from one side to the other 

 I have ventured to call " cross-education." 



The phenomenon was curious enough to suggest other experi- 

 ments. Another student. Miss T. L. Smith, was set to trying to 

 insert the point of a needle at the end of a rod into a small hole 

 in a drill-gauge without touching the sides. The first experiment 

 consisted of twenty trials with the left hand, with a success of fifty 

 per cent. Immediately thereafter twenty trials were made with 

 the right hand, with a success of sixty per cent. On the following 

 day and on each succeeding day two hundred experiments were 

 made with the right hand, with successes of 61, 64, 65, 75, 74, 75, 



