COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 65 



bluish at 40, and dark gray ( ?) at 50. The results of this experiment 

 are fully in accord with the findings of Adamiik and Woinow,* who 

 also report that the color of the after-images aroused at any retinal 

 region is complementary to the color of the primary sensation produced 

 at that region. Our results are further confirmed by the data contained 

 in a more recent paper by Walther.f 



All of this goes to show that the phenomena which we have de- 

 scribed in the foregoing pages as being characteristic of indirect vision 

 are similar in kind throughout to the phenomena of direct vision. The 

 whole retinal surface, with the exception of the macula and the blind- 

 spot, is endowed with a similar function, to the extent, at least, that no 

 region possesses a capacity which is wholly lacking in any other region. 

 The color sensitivity of the periphery is unquestionably less acute than 

 that of more central areas, and in consequence of this diminished sensi- 

 tivity a constant stimulus may arouse different sensations at different 

 regions. It can not, however, be said that any part of the normal retina, 

 save the macula and the blind-spot, is wholly or even partially color- 

 blind. For the whole manifold of sensation qualities which any region 

 is capable of furnishing may, under appropriate conditions of stimula- 

 tion, be furnished by every other region. 



Hellpach's discovery that a yellow stimulus gives no sensation of 

 yellow in indirect vision has not been confirmed by our results. Our 

 experience with the stimulus which he has called yellow in his paper 

 convinces us that Hellpach and the present writer differ in their employ- 

 ment of color names. But it is difficult to understand how this differ- 

 ence of terminology can account for his " discovery." For one can not 

 comprehend how any part of the spectrum can, under normal condi- 

 tions, appear more orange upon peripheral than upon paracentral re- 

 gions of the retina. And even the most distinctly orange stimulus must 

 appear yellow before it can pass over into gray in its progressive reces- 

 sion from the visual axis.J 



*Adamuk and Woinow. Beitrage zur T'heorie der negativen Nachbilder, 

 Graefe's Archiv., XVII, i, 1871, S. 141 f. 



t Anthon Walther. Beobachtungen iiber den Verlauf centraler und extra- 

 macularer Nachbilder, Pfliiger's Archiv., LXXVII, i and 2, 1899, S. 53-69. 



jThe recent testimony of Peters upon .this point -leaves no room for doubt 

 as to what are the facts of the case. Peters, who, it may be mentioned, worked 

 in tihe same laboratory as Hellpach, employed an exact duplicate of Hellpach's 

 yellow stimulus, and obtained results which support our findings as against Hell- 

 pach's. Peters found that .the stimulus in question (which Hellpach had 

 described as being composed of monochromatic light from the sodium line) was 

 frequently identified as yellow-orange in direct vision. He reports further that 

 it invariably appeared yellow upon the peripheral retina before passing over into 

 gray. Tihat is, it invariably appeared yellow when its luminosity was so weak 

 as to produce any marked change of tone in indirect vision. (W. Peters. Die 

 Farbenempfindung der Netzhautperipherie, u. s. w., Archiv fur die Gesamte 

 Psychologic, III, 1904, S. 374*-) 



