No. .)92] 



INDIVIDUAL DIFFERENCES 



223 



A maze, designed by Professor Cattell, was used, the 

 plan of which is shown in Fig. 1. The animal has in the 



first compartment the alternative between two gates, one 

 of which can be pushed open while the other is locked, and 

 then it has the same alternative in the second compart- 

 ment. When it takes the correct way in both compart- 

 ments, it finds itself in the food compartment. The path 

 that the animal must follow can be altered by changing the 

 gates which are locked. "Unit construction" is used in 

 the dimensions, which are adjusted to the size of the ani- 

 mal, and in the fact that any desired number of standard 

 units can be added. 



Preliminary tests were made with albino rats, but these 

 were given up for mice, which are more active and more 

 easily handled. The mice were given one trial each day, 

 and were tested at as nearly the same time as possible. 

 Light was found to play but a minor role in the tests, day- 

 light and artificial light serving equally well. At the out- 

 set the age of the mice when first tested was not always 

 known, but later when the various litters were obtained 

 the young mice were tested at or about four weeks old. 



The mice were rewarded for a successful trial by a mixed 

 diet of milk, bread, oatmeal and sometimes meat. They 

 alwavs had a little drv bread in their cages. Besides satis- 

 fying their hunger, the mice had the additional reward of 

 a place for exercise and the companionship of the mice 

 that had just been tested. The order of the tests was 



