14 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



A comparison of the sensations aroused by the same stimulus on 

 the central and the color-blind areas gave the following results : 



Color tone seen in direct vision. 



Spectral red (near end oi spectrum) 



Spectral yellow 



Spectral green (F-line) 



Spectral blue 



Spectral violet 



Sensation aroused upon 

 the " red-blind " zone. 



Dark gray. 

 Pale green.* 

 Light bluish gray. 

 Light greenish blue.* 

 Dark blue. 



*It will be seen that in two cases his stimuli appeared more greenish at the periphery 

 than at the fovea. This result has not been confirmed by other observers ; indeed there seems 

 to be no doubt that the opposite relation obtains. 



Experiments with mixed colors (pigments) gave the following: 



In direct vision. 



Red + ; blue 



Red + green. . . . 

 Green -f- blue. . . . 

 Blue + yellow. . . 

 Violet + yellow. 



In indirect vision. 



Appeared light bluish. 

 Appeared light 'grayish yellow. 

 Appeared ilight bluish. 

 Appeared bluish green. 

 Appeared marine 'blue. 



Schelske's investigation convinced him of the validity of the Helm- 

 holtzian theory of color vision, and of the existence of a zone of red- 

 blindness at the periphery of the retina. In common with Helmholtz 

 he assumed that every color stimulus in direct vision excites all three 

 sorts of color-sensing substance; in indirect vision only green-sensing 

 and violet-sensing substances are excited. This difference in the co- 

 operation of the visual substances in the two cases would, in the opinion 

 of Schelske, lead one to expect just such differences in color sensitivity 

 as are observed. 



The Helmholtzian principle was accepted and extended by 

 Woinow.* Employing pigment colors, this investigator observed the 

 following transitions of tone when the stimulus passed out into indirect 

 vision : Red becomes yellowish at but a slight distance from the fovea, 

 gradually passes over into yellowish-brown, which becomes darker and 

 darker, and finally black; if the background is much darker than the 

 stimulus, the latter appears light gray instead of black at the periphery. 

 Orange becomes yellowish, gradually grows murkier, and finally ap- 

 pears gray, light or dark according as the background is dark or light. 

 Yellow simply decreased in saturation until it appeared light gray at 

 the periphery. Green passes out through yellow or yellowish to gray ; 

 this stimulus never appears black at the periphery. Blue passes over 



*M. Woinow. Zur Farbenempfindung. Graefe's Archiv., XVI, i, 1870, S. 212-224. 



