2O COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



must be introduced into a rotating disc, in order that the color in ques- 

 tion may be perceived. His determination of liminal color stimulus 

 was made, not only for the fovea, but for various points upon the 

 peripheral retina, as well. He hoped by this means to obtain a quan- 

 titative expression of the relative sensitivity of various parts of the 

 retina to light of different color tones. Chodin remarks in his intro- 

 duction : " It is self-evident that in comparing the retinal sensitivity to 

 different colors, the color-stimuli employed must be of equal brightness 

 and of equal saturation."* But this very essential condition was not 

 fulfilled in his own experiments. His results are therefore invalid, in 

 so far as they refer to the relative sensitivity to different tones. 



They do show, however, that color sensitivity is invariably much 

 less at the periphery than at the fovea, the amount of decrease ranging 

 from 93 per cent (blue) to about 99.75 per cent (green). Chodin con- 

 fesses that he is unable to find a satisfactory explanation of this differ- 

 ence between direct and indirect vision. 



Klugf employed a gas spectrum and worked in a dark room. He 

 found blue to have the widest zone, then came green and yellow, then 

 red and orange, and finally violet. The color limits are extended by 

 brightening the stimulus and by increasing its area. Beyond the zones 

 of specific color sensitivity violet appears blue, orange appears yellow, 

 yellow appears green, while red, green, and blue undergo no change of 

 tone. Klug's explanation of these phenomena is similar to that of 

 Helmholtz. 



Charpentier J determined for various parts of the retina the minimal 

 visual angle at which a stimulus appears in its own color. He con- 

 cludes that all parts of the retina are most sensitive to blue, less to red, 

 and least to green. Color sensitivity is greatest at the center and de- 

 creases somewhat uniformly towards the periphery. With moderate 

 stimulation he found that the zone of blue has the widest extension and 

 that of green the narrowest ; but with appropriate increase of stimulus, 

 all colors may be recognized at the extreme periphery. All parts of the 

 retina are equally sensitive to white light ; and all respond to chromatic 

 stimulation with an initial sensation of pure brightness. This achro- 

 matic sensation persists only during the first instant of stimulation if 

 the color-stimulus possess more than a certain degree of brightness, but 



*Graefe':s Arehiv., XXIII, 3, S. 178. 



fF. Klug. Ueber Farbenempfindung foei indirectem Sehen, Graefe's Arehiv, 

 XXI, i, 1875, S. 251-294. 



JA. Charpentier. De la vision avec les diverses parties de la retine, Archives 

 de Physiologic, IV, 1877, pp. 894-895. Reprinted under same title, Paris, 1877. 

 La ilumiere et les couleurs, Paris, 1888. Landolt et Charpentier. Des sensations 

 de lumiere et de ooulenr, dans la vision directe et dans la vision indirecte, Comptes 

 Rendus, LXXXVI, 1878, pp. 495-497. 



