The Sense of Sight: Color Vision 135 



o 



the box until it found the food in the orange box. While it 

 was busily engaged in eating a piece of "force" which it had 

 taken from the box and - 



was holding in its fore 

 paws, squirrel fashion, 

 the color boxes were 

 quickly and without dis- 

 turbance shifted in the 

 directions indicated by 

 the arrows of Figure 18, 



1. Consequently, when 

 the animal was ready for 

 another piece of " force," 

 the food-box was in the 

 corresponding corner of 

 the opposite end of the 

 experiment box (position 



2, 18, II). After the 

 mouse had again suc- 

 ceeded in finding it, the 

 orange box was shifted 

 in position as is indi- 

 cated by the arrows in 

 Figure 18, II. Thus the 



tests were continued, the boxes being shifted after each 

 success on the part of the animal in such a way that for no 

 two successive tests was the position of the food-box the same ; 

 it occupied successively the positions i, 2, 3, and 4 of the fig- 

 ure, and then returned to i . Each series consisted of 20 tests. 

 An improvement on this method, which was suggested 

 by Doctor Karl Waugh, has been used by him in a study 

 of the sense of vision in the common mouse. It consisted 

 in the introduction, at the middle of the experiment box, of 



o', 



X 



1 



FIGURE 19. Food-box apparatus with mov- 

 able partitions. O, orange food-box; B, blue 

 food-box ; X, starting point for mouse ; A , point 

 at which both food-boxes become visible to the 

 mouse as it approaches them ; i, 2, two different 

 positions of the food-boxes; T, T, movable 

 partitions. (After Doctor Waugh.) 



