136 The Dancing Mouse 



two wooden partitions which were pivoted on their mid- 

 vertical axes so that they could be placed in either of the posi- 

 tions indicated in Figure 19. Let us suppose that a mouse 

 to be tested for color vision in this apparatus has been placed 

 at X. In order to obtain food it must pass through A and 

 choose either the orange or the blue box. If it chooses the 

 former, the test is recorded as correct ; if it goes to the blue 

 box first, and then to the orange, it is counted an error. While 

 the animal is eating, the experimenter shifts the boxes to 

 position i of Figure 19, and at the same time moves the par- 

 titions so that they occupy the position indicated by the dotted 

 lines. The chief advantage of this improvement in method 

 is that the animal is forced to approach the color boxes from 

 a point midway between them, instead of following the sides 

 of the experiment box, as it is inclined to do, until it happens 

 to come to the food-box. This renders the test fairer, 

 for presumably the animal has an opportunity to see both 

 boxes from A and can make its choice at that point of 

 vantage. 



Two males, A and B, of whose age I am ignorant, were 

 each given seventeen series of tests in the apparatus of 

 Figure 18. A single series, consisting of twenty choices, 

 was given daily. Whether the animal chose correctly or not, 

 it was allowed to get food ; that is, if it went first to the blue 

 box, thus furnishing the condition for a record of error, it 

 was permitted to pass on to the orange box and take a piece 

 of "force." No attempt was made to increase the animal's 

 desire for food by starving it. Usually it sought the food -box 

 eagerly; when it would not do so, the series was abandoned 

 and work postponed. " Force" proved a very convenient 

 form of food in these tests. The mice are fond of it, and they 

 quickly learned to take a flake out of the box instead of trying 

 to get into the box and sit there eating, for when they attempted 



