The Sense of Sight : Brightness Vision 129 



The critical comment which I wish to make for the benefit 

 of those who are working on similar problems is this. The 

 phosphor bronze wires, on the bottom of the electric-boxes, 

 by means of which an electric shock could be given to the 

 mouse when it chose the wrong box, are needless sources of 

 variability in the illumination of the boxes. They reflect the 

 light into the eyes of the mouse too strongly, and unless they 

 are kept perfectly clean and bright, serious inequalities of 

 illumination appear. To avoid these undesirable conditions 

 I propose hereafter to use a box within a box, so that the wires 

 shall be hidden from the view of the animal as it attempts 

 to discriminate. 



A brief description of the behavior of the dancer in the 

 brightness discrimination experiments which have been de- 

 scribed may very appropriately form the closing section of 

 this chapter. For the experimenter, the incessant activity and 

 inexhaustible energy of the animal are a never-failing source 

 of interest and surprise. When a dancer is inactive in the 

 experiment box, it is a good indication either of indisposition 

 or of too low a temperature in the room. In no animal with 

 which I am familiar is activity so much an end in itself as 

 in this odd species of mouse. With striking facility most 

 of the mice learn to open the wire swing doors from either 

 side. They push them open with their noses in the direc- 

 tion in which they were intended by the experimenter to 

 work, and with almost equal ease they pull them open with 

 their teeth in the direction in which they were not intended 

 to work. In the rapidity with which this trick is learned, 

 there are very noticeable individual differences. The pulling 

 of these doors furnished an excellent opportunity for the study 

 of the imitative tendency. 



When confronted with the two entrances . of the electric- 

 boxes, the dancer manifested at first only the hesitation caused 



