COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 4! 



the limits of the pairs of zones is due to the fact that the same visual 

 substance which gives rise to the sensation of red also produces the 

 sensation of green, while the substance which furnishes the sensation of 

 vellow also mediates the sensation of blue. 



The present status of the problem may be summarized as follows : 

 It has been established that color sensitivity decreases gradually from 

 the center to the periphery of the retina; that every color stimulus is 

 correctly recognized within a certain retinal zone, whose extent varies 

 directly with the tone, the brightness (absolute and relative), the satura- 

 tion, and the area of the stimulus, and with changing conditions of 

 adaptation and of refraction ; that under certain conditions the zone of 

 a certain red is co-extensive with that of a green, while that of yellow 

 is also co-extensive with that of blue ; that the yellow-blue zone, has a 

 much wider extension than the red-green zone ; that all colors, except- 

 ing the four mentioned above, pass through certain regular transitions 

 of tone as they appear upon more and more peripheral regions of the 

 retina; that these transitions tend in the direction of yellow (when red, 

 orange, or green stimuli are employed) and blue (when violet stimuli 

 are employed) ; and that with moderate stimulation all colors appear 

 gray at the periphery, while with a sufficiently intensive stimulation, 

 they may there appear in their own tones. 



There are, in the opinion of the writer, two features of this general 

 problem upon which it would be well to have additional light. It will 

 be remembered that Hellpach reports the discovery of an extreme peri- 

 pheral zone upon which all color stimuli tend to appear in their com- 

 plementary colors. Since this phenomenon has been reported by no 

 other investigator,* and since moreover it refuses to fit in with any of 

 the color theories now in the field, it seems desirable to work over the 

 ground covered by Hellpach with a view to discovering how his results 

 are to be explained. Then, too, the coincidence of the pairs of zones 

 which has been a characteristic of the findings of several recent investi- 

 gators has in every case been established for the light-adapted retina 

 alone. In view of the emphasis which in the recent literature is being 

 laid upon the differences between the phenomena of light-adaptation 

 and those of dark-adaptation, it seems distinctly worth while to deter- 

 mine whether this coincidence holds also for the dark-adapted retina. 



*Since the above was written Peters obtained somewhat similar results in 

 an exploration of the eccentric retina. 



