EXPLANATION OF OBSERVATIONS 175 



ment of this ability. We must bear in mind that in all 

 probability Mr. von Osten's movements -very gradually 

 became as minute as they are now, and that therefore 

 Hans at first learned to react to such as were relatively 

 coarse. Furthermore, his practice extended throughout 

 four years and during this time it was his sole occupation. 

 Without specific predisposition, however, all this practice 

 would have been utterly futile. We can also readily 

 appreciate how indispensable in the struggle for existence 

 a well-developed power of perceiving moving objects 

 must be to horses (and most other animals) living in 

 their natural condition and habitat, in order to be aware 

 of the approach of enemies, or, in the case of carnivora, 

 the presence of prey. In view of all these considerations 

 we can readily see how it was possible that the horse, 

 perhaps in spite of rather defective vision, could react 

 with precision to movement-stimuli which escaped ob- 

 servation by human eyes. 



We can understand also the horse's never-flagging 

 attentiveness when we recall that self-preservation 

 prompts eternal vigilance over against all that is going 

 on in the animal's environment. (In the case of Hans, 

 hunger was at first the motive ; later, habit did the work.) 

 Furthermore, the lower form is not hindered in giving 

 itself over to its sense-impressions by the play of ab- 

 stract thought which tends so strongly to direct inward 

 our psychic energy, — at least, in the case of the cultured. 



Nevertheless, Hans still remains a phenomenon not 

 only in excelling all his critics in the power of observa- 

 tion, but also in that he is the first of his species, in fact 

 the first animal, in which this extraordinary perceptual 

 power has been proven experimentally to be present. It 

 has long been known °^ that horses could be trained to 



