INTRODUCTION ii 



the truth, and whether it is enunciated by Aristotle or 

 Haeckel. 



Mr. von Osten, however, continued to exhibit Hans, 

 and is probably doing so still, but in what frame of mind, 

 I dare not judge. The spectators continue to look on, 

 they are doubly alert to catch movements, and many of 

 them have learned from Mr. Schillings what kind of 

 movements they are to expect. But these " initiated " 

 ones regularly return and declare that there is nothing in 

 the movements and that they simply could not discover 

 any aids given to the horse. Nothing can so well show 

 how difficult the case is, and how great the need of a 

 thorough exposition of the whole matter, than the ac- 

 count given in the following pages of Mr. Pfungst. Its 

 publication has been delayed on account of the additional 

 tests made in the laboratory, but we have reason to sup- 

 pose that through these additional tests the work has 

 gained in permanent value. Experimental psychologists 

 will perhaps be greatly interested in the graphic regis- 

 tration of the minute involuntary movements which ac- 

 company the thought process, and in the artificial asso- 

 ciation of a given involuntary movement with a given 

 idea. Likewise the tests on sense-perception in horses, 

 which have led to essential changes in hitherto current 

 views, and the critical review of the comprehensive litera- 

 ture on similar achievements of other animals, will be 

 welcomed by many. 



Before closing these introductory remarks, I would 

 make one more statement concerning Mr. von Osten. 

 The reader will notice that the judgment passed upon him 

 in this treatise is placed at the end, whereas in the report 

 of the commission it came first. This was brought about 

 by the change that was made in the way of stating the 



