EXPLANATION OF OBSERVATIONS 209 



tioned in Supplement III (page 255). — That many in- 

 dividuals were at first successful but were later unable 

 to get any successful responses, is to be accounted for by 

 the fact that the power of concentration, at first present, 

 later rapidly disappeared; ' "This "temporary increase in 

 the power of doing mental work was first investigated 

 experimentally by Rivers and Kraepelin,'^ and was called 

 by them " Antrieb " and aptly likened to the first pull of 

 a team of horses in starting off. This, too, explains an 

 experience which befell a number of the horse's visitors, 

 who later described it to me. Wishing to utilize a mo- 

 mentary absence of Mr. von Osten, they excitedly put a 

 hasty question to Hans, and with amazing regularity 

 received correct responses. — Besides Mr. von Osten, Mr. 

 Schillings and myself, not many were always able to in- 

 duce Hans to bring the colored cloths or to execute the 

 head movements. It was easy, on the other hand, to get 

 him to nod. Therefore there was some truth m Mr. von 

 Ostens' assertion, that Hans would be unable to answer 

 a difficult question if he had not previously indicated by 

 means of a nod that he had grasped its import. Those 

 who were not concentrating sufficiently, would not look 

 into Hans's face, when he was expected to nod, and 

 would not bend over, when Hans ought to begin tapping — 

 such persons could not, therefore, since they did not in- 

 duce Hans to nod, elicit the tapping. I, myself saw the 

 " no " successfully elicited only in the case of Mr. von 

 Osten, Mr. Schillings and Mr. Hahn ; the " right " and 

 " left " only in the case of the former two. It must re- 

 main uncertain whether this failure on the part of other- 

 wise suitable persons to elicit the responses for " right " 

 and " left " was due to their accompanying these ideas by 

 movements of the eyes instead of by movements of the 



