EXPERIMENTS AND OBSERVATIONS 73 



number 2, but without giving any voluntary sign of any 

 sort Hans tapped 2, wrhereupon Mr. Grabow put a 

 number of similar questions ; but I no longer thought of 

 the answers, and all of Hans's responses went wrong. 



Although Hans was not influenced by others so long as 

 a suitable experimenter was present, yet he might be 

 disturbed and under certain conditions might be led to 

 make the back-step in response to certain movements in 

 his environment. The person to whom he responded 

 would have to be close to the experimenter and would 

 necessarily have to execute a movement greater in extent 

 than the experimenter's. In such instances the raising of 

 the head, arm or trunk, was a sufficient stimulus. Thus 

 we made the following two series of tests. Mr. 'Stumpf 

 stood with trunk bent forward before the horse, and at 

 a moment decided upon beforehand, assumed an erect 

 position. I myself stood beside Hans and asked him to 

 tap. When I stood at the horse's neck, then Mr. Stumpf 's 

 interruption was effective. When I stood at the horse's 

 flank, the interruption effected only a seeming hesitation, 

 and when I moved still farther back, the horse continued 

 to tap despite any attempted disturbance. In the second 

 series the questioner remained constantly at the right 

 shoulder of the horse, while the one who attempted to dis- 

 tract him, changed positions. When the latter stood to 

 the right immediately in front of or beside the questioner, 

 the distrubance was effective in 10 out of 13 cases. But 

 when he stood back of, and to the right of, the questioner, 

 the attempts at disturbance were seldom successful. If 

 he chose a place before and to the left of the horse, there 

 was hardly any distraction (in 4 cases only, out of 13), 

 and if he stood to the left and behind the animal, he 

 exerted no influence whatever. Hans manifestly turned 



