The Sense of Sight: Brightness Vision 93 



tests. Figure 15 is its ground plan. This box, which was 



made of wood, was 98 cm. long, 38 cm. wide, and 17 cm. 



deep, as measured on the outside. ^^^^^^^^^^^^^^ 



The plan of construction and its 



significance in connection with 



these experiments on vision will 



be clear from the following ac- 



count of the experimental 



procedure. A mouse whose 



brightness vision was to be 



tested was placed in the 



nest- box, A (Figure 15). 



Thence by pushing open 



the swinging door at /, it 



could pass into the en- 



trance chamber, B. 



Having entered B it 



could return to A only 



by passing through 



one of the electric- 



boxes, marked W, 



and following the 



alley to O, where by 



pushing open the 



swing door it could 



enter the nest-box. 



The door at 7 SWUng doorway of right e lectric-box; E, exit from electric- 

 toward B, box to alley; /, swinging door between A and2J; 



O, swinging door between alley and ,4 ; 7C, induc- 



. ,-, . . ,. T , . . . . 



tion apparatus; C, electric cell; A, key in circuit. 



K 



O 



O 



FIGURE 15. Ground plan of discrimination 

 box. A, nest-box; B, entrance chamber; W, W, 

 electric-boxes; L, doorway of left electric-box; R, 



rmlv tVir>c^ at D 

 v-'iny . iiivjsc etc ^y . 



right and left, swung 

 outward, toward A, only. It was therefore impossible for 

 the mouse to follow any other course than A-I-B-L-W-E-O 

 or A-I-B-R-W-E-O. The doors at I and O were pieces of 



