174 



COLOUR VISION 



method, which agree with those already mentioned. We may more 

 conveniently discuss his results at a later stage (Part III). 



The spectrum as seen by the dark-adapted eye. Tschermak 1 has 

 stated that the process of adaptation varies according to the type of 



i Trichromats 



Deuteranope\ 



~| r Dichromats 



> Protanopes ) 



Brightness values of the energy 

 of the Spectrum 



670650 625 605 590 575 555 

 B C D 



535 520 505 

 E 



490 



Fig. 48. Photopic luminosity curves (intensity H) of triehromats and dichromats. 

 Abscissae, wave-lengths of the prismatic spectrum of gaslight; ordinates, arbitrary 

 scale. (Konig.) 



colour blindness, being normal in deuteranopes and much below normal 

 in protanopes. Nagel and v. Kries, however, are fully convinced that 



1 Arch. f. d. ges. Physiol. LXX. 297, 1898 ; Ueber physiol. u. path. Anpassung des Auges, 

 Leipzig, 1900 ; Ergeb. d. Physiol. I. 2, 700, 1902. 



