506 ADAPTATIONS TO PHOTIC QUALITY 



Nagel in 1902 and 1907, and Colvin and Burford in 1909. Lubbock, in 

 1888, Nicolai and Orbelli in 1907 and 1908, denied it. None of these 

 investigators adequately excluded discrimination on a basis of brightness. 

 Nor was brightness controlled properly by Kalischer, working in this 

 period, though he did use colored lights. One of his dogs could distin- 

 guish a red light readily from a blue one, less readily from other colors. 

 One reaction which Kalischer did obtain, and which speaks strongly for 

 a qualitative perception of hue, was a sharp withdrawal of the dog from 

 a blue light. 



The first impeccable experiments were those of Samoiloff and Pheo- 

 philaktova in 1907. They found that dogs confused colored papers with 

 gray ones of various shades; but they were not confused so consistently 

 as to make it certain that discrimination was wholly lacking. The best 

 results were obtained with green — the dog could not distinguish it readily 

 from dark grays, but showed some improvement with practice. When the 

 shape of the green paper was changed, the animal more often chose the 

 negative, gray paper which was of the old familiar shape. The investi- 

 gators concluded that form is far more important to the dog than color, 

 if indeed the animal experiences color at all. 



Smith, in 1913, worked with seven dogs which she also trained to col- 

 ored papers. For any given color, some group of grays in her long Nendel 

 gray series gave the dog great difficulty in discrimination; but Smith was 

 unable to find any gray which a given dog would always confuse with a 

 particular color. The animals could tell grays from each other better than 

 from colors; but Smith concluded that at least certain individual dogs 

 have an unstable color sense, so very rudimentary as to be completely 

 unimportant to the animal. For the dog, it is form and (to a less extent) 

 brightness which are important qualities of visual stimuli. Whatever 

 weakly chromatic sensations his cones may afford are further unsaturated, 

 greatly diluted, with 'grayness' stemming from his superabundant rods. 

 To any such semi-nocturnal, rod-rich animal, the richest of spectral lights 

 could at best appear only as delicate pastel tints of uncertain identity. 



For the domestic cat there is even less evidence of any color vision 

 whatever. Colvin and Burford, while they thought there was positive 

 evidence from their work in the case of the dog, claimed none for the cat. 

 De Voss and Ganson in 1915 reported a study of nine cats, in which 

 training to colored papers of controlled albedo and texture was involved. 

 For every cat and every color, a particular gray paper was found which 

 was completely confusing. When the training color was placed among 



