Cole and Long, Visual Discritniriation in Raccoons. 659 



from this box. N'ext they placed beside the first box two others like 

 it except that they bore disks cut from ISTendel's series of gray papers. 

 In order to get the food the dog must now discriminate the green disk 

 from the gray ones. At first the lightest grays were used. ITos. 1 

 and 2, then the darker ones in order up to ]^o. 50. In the first series 

 of 613 trials the dog made, on the average, 30 per cent of mistakes, 

 Avhile in the second series of 560 trials this was reduced to 10 per 

 cent. In the first series, grays ISTo. 17 and 'No. 18 were so often 

 confused with the green that the investigators at first thought the dog 

 was quite unable to make the discrimination. It was also only after 

 much training that he was able to distinguish the dark gray from the 

 green. So slow was his progress in learning that Samojloff and 

 Pheophilaktowa changed the question whether the dog discriminates 

 colors, to the question whether he can, after much practice, be brought 

 to do so. From the evidence of their records they answer this ques- 

 tion in the affirmative, but apparently not with perfect confidence. 



Orbeli used the salivary reflex method of Pawlow. By this method, 

 after the presentation of a particular stimulus has been repeatedly 

 accompanied by the act of feeding the dog, the presence of the 

 stimulus will cause a secretion of saliva. The amount of the secre- 

 tion and, to a less extent, its degree of viscidity, serve to indicate the 

 intensity of the stimulation. 



By means of a projecting lantern, visual stimuli were thrown on a 

 screen in front of the dog. Thus the animal's perception of form, 

 size, movement, brightness and color was tested. Images of various 

 colors (red, yellow, green, blue and violet) were received on the 

 screen. 



As to color vision, Orbeli derives the following conclusion from the 

 results of his experiments. '^A study of conditioned salivary reflexes 

 furnishes no indication that rays of light of different wave-length are 

 received as distinct stimuli by the eye of the dog. Conditioned 

 salivary reflexes are always determined by changes in the intensity 

 of light independently of its composition" (quality). 



Samojloff and Pheophilaktowa set out to answer two questions, 

 namely, (1) whether the dog discriminates colored from equally 

 bright gray objects, and (2) whether he discriminates equally bright 



