COLOR VISION 



885 



peculiar abridgments of the color field result in consequence of diseases 

 of the retina, and optic nerve or of lesions of the visual association area. 



Fig. 483. — Perimeter Chart Showing the Highly Restricted Color Fields in the 

 Left Eye of a Typical Case of So-called Red-green Color Blindness. (Howell.) 



Theories of Color Vision. — It has been pointed out above that the 

 rods and cones are somewhat different in their function. From the 

 standpoint of color vision it is now commonly believed that the former 



Fig. 484. — Diagram to Illustrate the Young-Helmholtz Theory of Color 

 Vision. Verticals Drawn at any Point of the Spectrum Indicate the Relative 

 Amount of Stimulation of the Three Substances for that Wave Length of the 

 Spectrum. (HelmhoUz.) 



which alone are present in the zone adjacent to the ora serrata, are 

 concerned with achromatic vision in low intensities of light, while the 

 latter are employed for color vision as well as for achromatic vision 

 in ordinary intensities of light. This conclusion, however, does not 



