172 The Dancing Mouse 



To test this conjecture two thicknesses of blue glass were placed 

 over one electric-box, two plates of green glass over the other ; 

 the incandescent lamps were then fixed in such positions that 

 the blue and the green within the two boxes appeared to the 

 experimenter, as he viewed them from the position at which 

 the mouse made its choice, of the same brightness. 



Mouse No. 2 was given two series of tests, series 18 and 

 19, under these conditions, with the result that he showed 

 absolutely no ability to tell the blue box from the green box. 

 The opportunity was now taken to determine how quickly 

 No. 2 would avail himself of any possibility of discriminating 

 by means of brightness. With the blue at 21 candle meters, 

 the green was increased to about 1800. Immediately dis- 

 crimination appeared, and in the second series (22 of Table 

 27) there were only two mistakes. 



The results of the blue-green experiments with light trans- 

 mitted from in front of the animal and from above it are in 

 entire agreement with those of the experiments in which 

 reflected light was used. Since the range of intensities of 

 illumination was sufficiently great to exclude the possibility 

 of blinding and of under illumination, it is necessary to con- 

 clude that the dancer does not possess blue-green vision. 



Again I must call attention to the fact that the behavior of 

 the mice in these experiments is even more significant of their 

 lack of discriminating ability than are the numerical results of 

 the tables. After almost every series of tests, whether or not it 

 came out numerically in favor of discrimination, I was forced to 

 add the comment, " No satisfactory evidence of discrimination." 



We have now examined the results of green-red, green- 

 blue, and blue-green tests. One other important combina- 

 tion of the colors which were used in these experiments is 

 possible, namely, blue-red. This is the most important of 

 all the combinations in view of the results already described, 



