COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 53 



SUMMARY OF GROSS RESULTS. 



These experiments show that, with slight luminosity of stimulus, 

 all colors appear colorless at the periphery of the retina ; that when they 

 are brought in far enough to appear colored, those of the red-end of the 

 spectrum first appear yellowish or yellow, while those of the blue-end 

 first appear bluish or blue ; and that in assuming their proper tones they 

 pass through a regular series of transitions. These transitions were so 

 pronounced that all observers were surprised to find that a constant 

 color stimulus could appear in such widely different tones. Indeed, it 

 frequently happened that an observer refused to believe that the objec- 

 tive conditions of stimulation had remained constant throughout the 

 series. The changes of color tone reported were : 



(1) Red first appeared yellowish, then passed through yellow, 

 orangish-yellow, yellow-orange, orange, and orange-red before it finally 

 appeared red. 



(2) Orange came in yellowish, gradually assumed a more and 

 more orangish tint, and finally appeared orange or reddish-orange. 



(3) Yellow first appeared yellowish, gradually increased in satura- 

 tion, and became orangish towards the center of the retina. This 

 stimulus really contained an orangish tint. 



(4) Green appeared yellowish at first, gradually increased in sat- 

 uration, and towards the close of the series assumed a greenish, and 

 finally a green tint. 



(5) Blue underwent no appreciable change of tone, but became 

 more and more saturated as the series progressed towards the fovea. 



(6) Violet appeared bluish, then blue, and took on a violet tint 

 very much later. Indeed, it sometimes happened that the violet tone of 

 this stimulus was not recognized at ten degrees from the visual axis. 



(7) Purple gave the longest and richest series of transitions. Be- 

 ginning with yellowish, its tone gradually moved down the spectrum, 

 passing through orange-yellow, yellow-orange, orange, orange-red, red, 

 purplish-red, and reddish-purple, before the pure tone of the stimulus 

 finally appeared. 



A comparison of the two sets of results (obtained with different 

 luminosity of stimulus) shows that the retinal zones of sensitivity ex- 

 pand with increase of intensity of stimulation. To what degree this ex- 

 pansion may be brought about by appropriate variation of stimulus can 

 not be decided definitely from these experiments. Yet it seems safe to 

 infer that if the stimulation be sufficiently intensive, all colors may be 

 recognized at the extreme periphery. Indeed, an attempt was made in a 

 series of subsidiary experiments to test the validity of the Exner- 

 Landolt principle. When the luminosity of the stimuli was increased it 



