86 The Dancing Mouse 



tions were recorded. The five individuals of the litter, four 

 females and one male, were taken from the nest one at a 

 time at 7 A.M. and placed on a piece of paper in the bright 

 sunlight. The warmth of the sun soon quieted them so 

 that auditory tests could be made to advantage. As soon as 

 an individual had become perfectly still, the Galton whistle 

 was held at a distance of about four inches from its head in 

 such a position that it could not be seen nor the currents of 

 air caused by it felt, and suddenly blown. Each of the five 

 mice responded to the first few repetitions of this stimulus by 

 movements of the ears, twitchings of the body, and jerky 

 movements of the legs. The most violent reactions resulted 

 when the individual was lying on its back with its legs ex- 

 tended free in the air. Under such circumstances the four 

 legs were often drawn together suddenly when the whistle 

 was sounded. Similar responses were obtained with the lip 

 sound already mentioned. Two other observers saw these 

 experiments, and they agreed that there can be no doubt that 

 the mice responded to the sound. The sounds which were 

 effective lay between 5000 and 10,000 complete vibrations. 



On the fifteenth day the eyes were just beginning to open. 

 Three of the mice responded definitely to the sounds, but the 

 other two slightly, if at all. On the sixteenth day they were 

 all too persistently active for satisfactory auditory tests, and 

 on the seventeenth, although they were tested repeatedly 

 under what appeared to be favorable conditions, no signs of 

 sensitiveness were noted. Although I continued to test this 

 litter, at intervals of three or four days, for two weeks longer, 

 I did not once observe a response to sound. 



This was the. first litter with which I obtained perfectly 

 definite, clear-cut responses to sounds. That the reactive 

 ability had not been present earlier than the fourteenth day 

 I am confident, for I had conducted the tests in precisely 



