40 



COLOUR VISION 

 B 



49 50 51 52 53 54 55 56 57 58 " 

 Fig. 9. Colour triangle. W, white ; R, red ; G, green ; B, blue. The numbers are those 

 of an arbitrary scale of the spectrum of the arc light. (Abney and Watson.) 



The Influence of Macular Pigmentation. The macula lutea, as its 

 name implies, is permeated with a yellow pigment, and therefore absorbs 

 certain spectral rays more than others. The variations in colour 

 matches and in the estimation of complementary colours by various 

 normal-sighted individuals were attributed by Maxwell 1 to this cause. 

 Glan 2 and Sachs 3 examined the absorption of the yellow pigment 

 from the macula of human eyes. Sachs found that absorption is 

 inappreciable in the red and orange, commences in the yellow-green 

 and gradually increases towards the violet end. Moreover, the amount 

 of pigment varies considerably in different individuals. Sachs examined 

 nine specimens : the mean coefficients of transmission of monochromatic 

 lights of these cases are as follows (Krarup) 4 : 



1 Phil Trans. Roy. Soc. Lond. CL. 57, 1860. 



2 Arch. /. d. gcs. Physiol xxxix. 53, 1886. 



3 Ibid. L 574, 1891. 



4 Loc. cit. p. 18. 



