144 CALVIN P. STONE 



as well, which are not aggressive or are on the verge of sexual 

 impotency. On several occasions aggressive adult males were 

 seen copulating repeatedly with lethargic females, whereas other 

 potent but less aggressive adults made no attempts whatever. 



Practical application of the foregoing discovery was made in 

 an endeavor to provide artificially a movement-stimulus which 

 would serve as an inducement for the young to attempt copu- 

 lation with a non-receptive rat from which none of the odors 

 characteristic of the female in heat emanated. In this way it 

 seemed probable that some evaluation of the importance of the 

 movement-stimulus could be made in the absence of the olfac- 

 tory stimulus. 



A female, having been tested and found unreceptive, was 

 made extremely sensitive to touch in the vaginal region by paint- 

 ing the root of the tail and the ano-vaginal zone with a very 

 weak solution of hydrochloric acid. She was then placed with 

 a vigorous young male seventy-eight days of age which had not 

 had previous experience in copulation. In a short time the male 

 began nosing and licking in the vaginal region. The female 

 responded to these tactile stimuli applied in the hypersensitive 

 vaginal zone by jumping away from him. Signs of sexual ex- 

 citement with a tendency to follow appeared at once in the male. 

 This mild excitement and sexual aggression was continued for a 

 few minutes with no accentuation until finally the female upon 

 being touched darted forward suddenly in the cage away from 

 the male. He pursued instantly and, overtaking her with a 

 few bounds, performed the complete copulatory act insofar as 

 this was possible without the cooperative action of the female. 

 He repeated the act again and again before the female was re- 

 moved from the cage. Similar responses were obtained with 

 another young male by modifying, in a similar manner, the 

 behavior of a non-receptive female so that it resembled the 

 characteristic behavior of the receptive female. 



In another instance, a young female guinea-pig, whose size 

 approximated that of an adult rat, was placed into the cage of an 

 inexperienced male seventy-four days of age. This rat had been 

 reared in isolation from the age of thirty-five days. Although he 



