84 EVOLUTION OF THE HUMAN EYE 



Miss E. M. Smith, 40 from an elaborate series of experi- 

 ments on dogs, summed up her conclusions as follows: 



"1. That while evidence has been obtained to show t ha t 

 some dogs possess a rudimentary power of color discrimi- 

 nation, such discrimination is highly unstable and cannot 

 be supposed to play any part in the animals' normal exist- 

 ence. 



"2. That the color-sense is, as shown by the high color 

 threshold, very weak. 



"3. That color discrimination, even where clearly 

 established, may be readily inhibited -by differences of 

 luminosity or position." 



Kinnaman 41 carried out experiments on monkeys with 

 food in glass tumblers covered with different colored cards, 

 and came to the conclusion that their capacity to distinguish 

 color as such was undoubted. 



Dahl 42 colored some sweets and some bitter substance 

 with different colored dyes; he found that after a few 

 attempts a monkey learned to leave without even tasting 

 those which were colored with the dye indicating a bitter 

 substance, and to seize at once upon those colored to indicate 

 sweets-. Varying the experiments sufficiently he found that 

 the monkey distinguished all the different colors readily 

 except dark blue. 



Hess 43 tested a monkey in the following manner: Grain 

 was scattered over a black surface upon part of which a 

 Spectrum was thrown. The monkey gathered all the grains 

 fn tin the extreme red to the extreme violet, leaving those 

 unilluuiinatcd. When the animal was dark-adapted and 

 the intensity of the light diminished until the grains were 

 visible to the dark-adapted experimenter only in the yellow 

 and green, only those grains were gathered. Hess con- 

 cludes that the extent of the spectrum is the same tor the 



