344 



WALTER S. HUNTER 



room on the first day in order to be certain that the darkness would 

 not disturb the reaction. On the following day the rat was 

 placed in the apparatus with the room dark and the light at 

 turned on. A correct response consisted either of running to the 

 right for the light or to the left for darkness. As the table indi- 

 cates, rat 46 failed to make the substitution, making only 5 < or- 

 rect reactions out of 10 on each of two days with the light. This 

 was mere chance. Rat 47, on the other hand, made the substi- 

 tution on each of three days, making 9, 8, and 9 correct reactions 

 respectively. 



TABLE 2 

 Data on light substitution 



These results indicate clearly a greater similarity, for the be- 

 havior of rat 47, between noise and light than was found between 

 noise and tone. This is harmonious with the apparent fact of 

 insensitivity to the tones as indicated in the earlier papers. 



Five rats, 1, 7, 9, and 11, had been trained in 1915 to discrimi- 

 nate handclapping from silence, using the same apparatus, by 

 running to the right for handclaps and to the left for silence. (A 

 description of this work is published in the 1917 article.) No 

 direct tests were made on their ability to substitute tones for the 

 noise. It is legitimate to assume that, like all of the many rats 

 heretofore tested, they would have failed. They were tested 

 however upon their ability to substitute a tactual and a visual 

 stimulus for the noise. For the tactual stimulus a piece of coarse 



