COLOR BLINDNESS OF CATS 119 



We began this investigation with the intention of studying 

 the vision of the cat under both daylight and twilight illumination, 

 thus planning to use both reflected and transmitted light. Some 

 work was done on the dark-adapted eye with filtered light, 

 and we hope to carry the investigation further. At present 

 we can report only the results obtained under light adaptation 

 and by the use of colored papers. The enormous variation 

 in the size of the cats' pupils suggested the possibility that 

 this is a device which keeps the retina always in twilight. But 

 as yellow, apparently, is the brightest of the colors for the cat 

 as well as for the human eye, under light adaptation, the possi- 

 bility of the animal's possessing twilight vision alone is very 

 doubtful. 



Three female and six male cats were tested. There is abundant 

 evidence that these cats represented entirely non-related strains. 

 Each cat was given from thirty to one hundred twenty trials 

 a day according to his degree of hunger. One cat was given 

 fifteen thousand trials and the trials of all the cats number over 

 one hundred thousand. 



By taking care not to over-feed the animals they were kept 

 (with one exception) in excellent health throughout the progress 

 of the experiments. The cats often purred during the experi- 

 ments, which perhaps indicates that the conditions were not 

 sen ously ' ' artificial ' ' . 



The colors were presented in pairs and each cat was given 

 preliminary training with easily discriminable pairs until his 

 selection of the "food color" or stimulus color was rapid and 

 accurate. Since most of the pairs were readily discriminated 

 no cat reached a "confusion area" until he had been thoroughly 

 trained in the experiment. With one animal we would begin 

 at the red end of the Bradley series. With the other, which 

 was to confirm or refute the results gained with the first, we 

 began at the violet end, and so on. Since red is known to 

 have a low stimulating power in the case of mice, rabbits, etc., 

 we began our experiments with yellow and blue as stimulus 

 colors. 



From the beginning our object was to search systematically 

 for confusions between a gray and a color, or between two colors, 

 without any preconceived theory as to where, in the series, 

 such a confusion might occur, or even whether it might occur 



