DICHROMATIC VISION 



175 



adaptation occurs exactly as in the normal in all types of colour 

 blindness. 



It has already been mentioned that the achromatic scotopic 

 luminosity curve is identical with the normal in all cases of colour 

 blindness. 



With regard to Purkinje's phenomenon, owing to the relatively 

 far greater ratio of the achromatic scotopic values of the yellow-green 

 region of the spectrum to the red as compared with normal vision all 



10 



15 20 25 30 35 40 45 50 



Scale of Prismatic Spectrum. 



55 60 



65 



Fig. 49. Photopic luminosity curves of trichromats and dichromats. (Abney.) 



the effects are accentuated. This fact was early brought out by 

 Preyer 1 and van der Weyde 2 and more conclusively by Konig 3 . Thus 

 Konig found a change of maximum brightness from 605 (JL/JL to 535 ^ 

 for the deuteranope Brodhun and from 575 ^ to 535 ////, for the 

 protanope Ritter on diminution of the intensity of the light, associated 

 of course with increasing dark adaptation. Konig and Tonn made a 



1 Arch.f. d. ges. Physiol. xxv. 31, 1881. 2 Arch.f. Ophth. xxvm. 2, 1, 1882. 



3 Konig and Brodhun, Sitz. d. Akad. d. Wiss. Berlin, 311, 1887 ; Brodhun, Zlsch. /. 

 Psychol. u. Physiol. d. Sinnesorg. v. 323, 1893 ; Tonn, op. cit. vn. 279, 1894. 



