132 The Animal Mind 



often evidenc ed in bird song are proof that this is the case.^ 

 Craig (157, 158) has carefully observed the social significance 

 of a great variety of sounds made by pigeons, but gets little 

 evidence that these birds learn new sounds by imitation. 

 Extremely significant are Hunter's (353, 354) experi- 

 ments on the hearing ability of the white rat. Their 

 net result is that these animals can he ar only noises, 

 not tonep. None of the rats he tested was able to hear 

 a tuning fork tone ; the evidence is that they were unable, 

 under the stimulus of both punishment and reward, to 

 learn to turn to the right when the tone was sounded 

 and to the left when it was not sounded. They could 

 perfectly well acquire such a habit when the noise of clap- 

 ping the hands was substituted for the tone. They could 

 not form the habit when two forks of different pitch were 

 sounded together as a signal to turn to the right. They 

 acquired the habit of making the proper response when the 

 tones of a whistle were substituted for the fork tones, but 

 it was clear that they were really responding to the noise 

 of the rush of air through the whistle, for they would 

 react equally well when this noise was substituted for the 

 actual blowing of the whistle. Moreover, they broke 

 down in their choices when the whistle was sounded in 

 another room, although they were not disturbed by the 

 mere diminution of intensity in the sound of the whistle 

 sounded near at hand; the natural inference is that re- 

 moving the whistle to a distance made the noise accom- 

 panying its tone inaudible. In short, there seemed to be, 

 for these rats, no difference between the sound of a pure 

 tone and entire silence. Confirmatory results appear in 



* Interesting evidence of this power in a bird which might not have been 

 supposed to possess it was obtained by Conradi, who found that English 

 sparrows reared by canaries acquired recognizable bits of the canary song 

 (141). 



