EXPLANATION OF OBSERVATIONS 163 



conditions* We know nothing regarding chromatic 

 vision in the horse, though we have often had trained 

 horses which apparently possessed color discrimination. 

 The earliest report of this kind I find in a work published 

 in the year 1573.^" Here we read that a number of 

 Germans exhibited two horses in Rome which could, 

 upon request of their masters, point out those persons 

 among the spectators who were wearing stockings of 

 any designated color. The passage, " conoscevano i 

 colori ", (they recognized the colors,) proves nothing and 

 no one has ever heard, even in modern times, of a horse 

 that actually knew colors. 



Nor did Hans possess anything like that high degree 

 of visual acuity which had been attributed to him. He 

 was supposed to be able to read easily at a distance small, 

 almost illegible script, which we ourselves could decipher 

 only with the greatest difficulty close at hand. It was 

 also supposed that he could distinguish ten- and fifty- 



* All told, there are hardly more than half dozen experimental inves- 

 tigations of the color-sense in mammals, — to speak only of these. 

 ■ Three of them deserve especial mention. One, the work of the Amer- 

 ican, Kinnaman, " on two Rhesus monkeys. Then a brief but careful 

 piece of work by Himstedt and Nagel.'* These two investigators were 

 able to determine that their trained poodle could distinguish red of any 

 tone or shade from the other colors, and from Professor Nagel I learned 

 that later the tests were extended and the same was shown to be true 

 concerning the blue and the green. And finally there is an investiga- 

 tion which hitherto has been known only from a reference which Pro- 

 fessor Dahl,25 the investigator, himself makes. The work is on a mon- 

 key, Cercopithecus (Chlorocebus) griseoviridis Desm. (Professor 

 Dahl has kindly allowed me to look over the records of the experi- 

 ments. He intends to publish the monograph at an early date.) 



All of these investigators arrive at the conclusion that the animals 

 tested by them possess color-sense. The monkey last-mentioned shows 

 one peculiarity : it was unable to distinguish a saturated blue from the 

 black. It will require further tests to clear this up. 



