AUDITORY SENSITIVITY OF THE WHITE RAT 349 



pended above the apparatus in a manner which prevented the 

 transmission of vibrations directly to the box. When the metro- 

 nome was used, it was placed upon a ledge just to the back and 

 above the apparatus and entirely separated from direct connec- 

 tion with the experimental table. The forks used (mounted 

 upon resonance boxes) were suspended in the same manner as 

 the buzzer. In controls 13 to 18 a strip of metal was fastened to 

 the spindle of a motor in such a manner that the rotations of 

 the motor caused it to strike at a definite rate against a card- 

 board. This gave an excellent noise of medium intensity and of 

 volume and quality different from the handclaps. The motor 

 (a silent one) was placed upon a nearby table. 



The results secured are summarized in table 4. Rat 7, who 

 was tested with the beats from the forks, ignored them and would 

 not class them either with the continuous or with the inter- 

 rupted noises. Hissing and the "rush of air" sound were sub- 

 stituted readily for the buzzer, i.e.j at least 80 per cent correct 

 reactions were made going to the left for these noises and to the 

 right for silence. The metronome beating at 120 and at 176 

 were substituted for the handclap successfully; whereas the rat 

 persistently refused to run to the right for the metronome at 200 

 and to the left for silence. Two 512 v.s. forts mistuned to give 

 beats of 142 and 174 per minute were ignored as were the beats 

 from the forks 512 v.s. and 576 v.s. sounding together. The 

 evidence suggests that the rat was insensitive to the beats, which is 

 very interesting inasmuch as beats are periodic variations in inten- 

 sity and the rats seem insensitive to tone. The evidence also indi- 

 cates that the transition between continuous and intermittent 

 noises occurs in the region of 200 interruptions per minute. 



Rat 27 ran to the left for hissing, and for the motor knocking 

 at the rate of 500 per minute. It refused to go to the left for the 

 motor knocking at .the rate of 232 per minute and for the metro- 

 nome at 200 per minute (right for silence). The motor rate of 

 250 was neither clearly rejected from nor clearly included with 

 the continuous sounds. The rates of 120 and 180 per minute 

 were definitely substituted for the handclaps, whereas hissing, the 

 buzzer, and the metronome at 160, 200 and the motor at 240 were 



