No. 486] THE PROBLEM OF COLOR VISION 377 



intersection of the blue with the green and red curves respectively. 

 In the absence of the blue substance, the white band is near the 

 yellow. This accords with the observations upon the color blind. 

 The absence of the green substance would not shorten the spec- 

 trum, but the lack of the red or blue would cut off their respective 

 ends. All of these features are equally well explained if, instead 

 of the absence of one of the three substances, such a modification 

 of its reaction is assumed as would be illustrated by a lateral 

 shifting of its curve in the diaoram. Thus in red blindnf>s the 

 red curve is shifted to cover more closely tiie territory of the ureen; 

 in green blindness the green is shifted toward the red; and in blue 

 blindness the blue and green curves are brought together. Thus 



in the color blind all three substances are pres 

 form. Since this modified Young-Helmholtz 

 well with observations on color blindness, it is o 

 as the most satisfactory explanation of color \ 

 An interesting attempt has been made by 1 

 theory into relation with structural elements 

 believes that thcvisual cells of invertebrates a 

 a fibrillation which is transverse to the direct 

 light waves, and that the tendency of the v 

 cones to separate into lran>verse dix - is evi 

 structure. Many hundreds of >nch fil)rils n 



