1 1 2 The Dancing Mouse 



ability was olfactory rather than visual. As precautions 

 against this possibility the cardboards were renewed fre- 

 quently, so that no odor from the body of the mouse itself 

 should serve as a guiding condition, different kinds of card- 

 board were used from time to time, and, as a final test, the 

 cardboards were coated with shellac so that whatever charac- 

 teristic odor they may have had for the dancer was dis- 

 guised if not totally destroyed. Despite all these precautions 

 the discrimination of the boxes continued. A still more con- 

 clusive proof that we have to do with brightness discrimina- 

 tion, and that alone, in these experiments is furnished by the 

 results of white-black tests made with an apparatus which 

 was so arranged that light was transmitted into the two 

 electric- boxes through a ground glass .plate in the end of 

 each box. No cardboards were used. The illumination of 

 each box was controlled by changes in the position of the 

 sources of light. Under these conditions, so far as could be 

 ascertained by critical examination of the results, in addition 

 to careful observation of the behavior of the animals as they 

 made their choices, there was no other guiding factor than 

 brightness difference. Nevertheless the mice discriminated 

 the white from the black perfectly. This renders unneces- 

 sary any discussion of the possibility of discrimination by 

 the texture or form of the cardboards. 



Since a variety of precautionary tests failed to reveal the 

 presence, in these experiments, of any condition other than 

 brightness difference by which the mice were enabled to 

 choose correctly, and since evidence of ability to discriminate 

 brightness differences was obtained by the use of both re- 

 flected light (cardboards) and transmitted light (lamps 

 behind ground glass), it is necessary to conclude that the 

 dancer possesses brightness vision. 



