104 



The Dancing Mouse 



sented as conclusive proof of discrimination, it must be 

 shown that the mouse has no preference for the particular 

 brightness which the arrangement of the test requires it to 

 select. That any preference which the mouse to be tested 

 might have for white, rather than black, or for a light gray 

 rather than a dark gray, might be discovered, what may be 

 called preference test series were given before the discrimi- 

 nation tests were begun. These series, two of which were 

 given usually, consisted of ten tests each, with the white 

 alternately on the left and on the right. The mouse was 

 permitted to enter either the white or the black box, as it 

 chose, and to pass through to the nest-box without receiving 

 a shock and without having its way blocked by the glass 

 plate. The conditions of these preference tests may be 

 referred to hereafter briefly as "No shock, open passages." 



TABLE 7 

 BRIGHTNESS DISCRIMINATION 



White-Black, Series n 

 Experimented on No. 5 February 2, 1906 



