THE PROBLEM OF COLOR VISION 



JOHN M. DAXE 



The problem of color vision is one of the most intricate which 

 the biologist is asked to solve. The following paragraphs are 

 intended to indicate the several methods which are being employed 

 for its solution, together with some of the results thus far obtained. 

 The anatomy of color vision will be considered first; then in turn 

 its physiology and its development; and finally, the abnormal 

 conditions of color blindness, together with the theories of normal 

 vision to which they have given rise. 



Anatomy. The mechanism of color vision is lodged in the rod 

 and the cone cells. A ray of light, after passing through the 

 lens of the eye and its vitreous body, penetrates several layers of 

 the retina, thus arriving at the proximal ends of the elongated 

 rod and cone cells. These cells are arranged in a single row. 

 The light traverses the length of the cells to their distal ends which 

 it stimulates. The rod and cone cells project against a single 

 layer of heavily pigmented cells, the stratum pigmenti retinae 

 (Fig. 1, S. P.). These have non-retractile processes which are 



the f<)nn of'donljlttMllVn-vs!^^^ .ranules. niiurat.-s into th'ese 

 processes when the eye is illinninated ; in ilie dark it i> withdrawn 

 into the cell body. 



Every rod cell consists of a rod, a rod fiber, and a nucleus, 

 arranged as shown in Fig. 1, A. A rod, which is from 40 to 50 // 

 long and L5 to 2 ri in diameter, consists of a doubly refractive, 

 lustrous oiifcr scqment, and a singly refractive, finely granular 

 nnur .se<jmn,f. In serum or dilute osniie aeid the outer segment 

 breaks into a series of regular transverse discs which are lu'lieved 

 to indicate a stratified structtu-e in the living rods, \ isual pin-ple 

 is a pigment which occurs only in the outer segments of the rods. 



365 



