COLOR-SENSE 91 



visions of Turner! If man, base as he yet is, can neverthe- 

 less rise today in his highest moments so far above his 

 sensuous self, what may he not hope to achieve hereafter, 

 under the hallowing influence of those chaster and purer 

 aspirations which are willing up within him even now^ toward 

 the perfect day!" 



It would be interesting to be able to correlate with these 

 views on the evolution of color-sense definite changes in 

 the structure of the retina. Such knowledge as we at 

 present possess permits of this being done in only a tentative 

 manner. The color-sense in man, like the form-sense, is 

 most acute at the macula, where cones only are present. 

 Though the final appreciation of both form and color is 

 evidently a psychological process, it seems to be an essential 

 preliminary step in such appreciation for some change to 

 take place in the end-organs of the nerve fibers in the retina. 

 That the change which gives rise to the sensation of form 

 is essentially different from that which gives rise to the 

 sensation of color is shown by the fact that the one may be 

 deficient without the other being impaired. In cases of 

 congenital amblyopia the form-sense is defective while the 

 color-sense is normal, and in the case of congenital dichro- 

 rnats the color-vision is defective while the form-sense is 

 normal. 



The essential factor in the perception of color must be 

 due to some at present unknown reaction, which waves of 

 light of varying wave-lengths produce in the individual 

 cones. As the perception of hues is more acute at the 

 macula than elsewhere, we may infer that the cones in that 

 situation are more capable of undergoing this unknown 

 reaction than those situated in the more peripheral parts 

 of the retina. A comparison of the microscopical appear- 

 ances of the cones at the macula with those at the periphery 



