132 COLOUR VISION 



The most recent and most exhaustive experiments have been made 

 by Hess^. 



Mammals. Graber^ experimented on nine dogs by his " preference 

 method." A j^oodle and a fox terrier showed definite preferences. 

 When black and white were presented white was chosen 56 times, 

 black 4 : when light red and blue, blue 53 times, red 7 ; when the same 

 and a much darker blue, blue 32 times, red 28. The results may have 

 been due to preference for the brighter colour. Lubbock^ experimented 

 with a poodle. Three pairs of cards coloured blue, yellow, and orange, 

 were used. One card from each pair was placed on the floor and the 

 remaining card of one of the pairs shown to the dog in the hope that 

 she would learn to select from the three cards before her the one that 

 was of the same colour as that held up. Training for ten weeks proved 

 entirely without success. Lubbock himself remarks that negative 

 results prove nothing as to the colour vision of the animal. Himstedt 

 and Nagel* taught a poodle to fetch coloured balls. On being ordered 

 to fetch " red " it brought first scarlet or bright red, then orange, but 

 only the latter when there were no more conspicuous red balls left. 

 Balls coloured with Bismarck brown were a cause of difficulty to it. 

 " Blue and grey were obviously quite different to it from red, even in 

 all degrees of brightness of each." 



Elmer Gates^ experimented with dogs and food receptacles of 

 various colours, including grey ; only receptacles of one particular 

 colour actually contained food. In some experiments coloured metal 

 plates were laid on a passage, certain colours being connected with a 

 battery, so that if the dog stepped upon them it received a shock. 

 Gates concluded from his researches that dogs could distinguish not 

 only colours but relatively fine difl^erences of hue. The description is 

 so meagre that it is impossible to determine whether due precautions 

 were observed. 



Samojloff and Pheophilaktowa*" tested whether a dog could be taught 

 by much training to distinguish between different colours as well as 

 between different brightnesses. Three boxes were placed in a row ; 



1 Vcrglcichende Physiolofjie des Gcsichisinnes, Jena, 1912 (Bibliography) : " Birds " — 

 Arch. /. Augenhlk. lvii. 4, 298, .317, 1907; Lix. 2, 142, 1908 : " Fishes "—Zoc. cit. lxiv. 

 Erganzungsheft, 1, 1909; Arch. f. d. ges. Physiol, cxxxiv. 1910; cxlii. 1911; Zool. 

 Jahrb. 1912; " Eeptiles and Amphibia" — Arch. f. d. ges. Physiol, cxxxii. 255, 1910. 



- Grv.ndlinien zur Erforschung des Helligkeits- u. Farhciisiiines der Thiers, Prag, 1884. 



' On the Senses, Instincts, and Intelligence of A)nmah, p. 280, Londoji, 1888. 



* Festschrift d. Univ. Freiburg, 1902. = The Moni.sf, p. 574, 1895. 



8 Centralhl. f. Physiol, xxi. 133, 1907. 



