184 COLOUR VISION 



equally manifests itself with paracentral fixation. There might, 

 however, be more widespread dense macular pigmentation or pigmen- 

 tation of the refractive media. This possible factor can be tested by 

 comparison of the achromatic scotopic values of spectral lights for a 

 normal and an anomalous trichromat with a fixed blue (460 (jlix) 

 comparison light. The ratios of the quantities of blue to match the 

 homogeneous lights for Halben (normal) and Lotze (partial deuteranope) 

 were 



The difference is therefore not due to more extensive pigmentation. 



As might be expected the luminosity curves of the anomalous 

 trichromats show corresponding differences from the normal (Watson^). 

 It has already been mentioned {v. p. 179) that v. Maltzew^ found 

 individual variations in trichromats, and these formed a complete 

 series between the trichromats and complete deuteranopes by way 

 of the partial deuteranopes. The protanopes and partial protanopes 

 showed a quite different luminosity distribution. In red-green mixtures 

 the red component is much more powerful than the green. She con- 

 cludes that the differences in colour matches between the normal and 

 the anomalous have a different cause from the individual variations 

 of the normal. The latter correspond with the luminosity differences, 

 whereas the former do not. 



Guttmann^ has made important contributions to the knowledge 

 of anomalous trichromatic vision. He is himself a partial deuteranope. 

 He finds that anomalous trichromats show seven chief differences from 

 normal trichromats. 



(1) For partial deuteranopes the discernible difference in hue is 

 smaller in the yellow and greater in the green than for the normal. 

 The difference in the green is not marked, but that in the yellow 

 is very appreciable. Guttmann's mean error {v. p. 19) at 589 /xfi 

 was from 12 to 13 /x/x, whereas that for the normal under like conditions 

 was 1 to 2 fx^. 



(2) The anomalous deuteranopes are more dependent on intensity. 



1 Proc. Roy. Soc. Land. A, Lxxxvm. 1913 ; see Part III. 



2 Ztsch. f. Sinnesphysiol. xun. 76, 1908. 



3 Neurol. Centbl. 491, 1904; Ztsch. f. Sinnesphysiol. xlh. 24, 250, 1907 ; XLm. 146, 

 199, 255, 1908-9; Munch, med. Wochenschr. 566, 1910 ; Ztsch. f. Sinnesphysiol. l\ti. 271, 

 1910. 



