SENSE ORGANS. 



139 



Mrs. Franklin has recently brought forward a view 

 which deserves and has received much attention. She 

 thinks that color perception, like all other faculties, has 

 been gradually evolved. The steps were as follows: 

 First of all, in the early stages of evolution there was 

 but one color-substance in both the rods and the cones 

 This she calls gray color-substance, because it is photo- 

 chemically affected by, and gives rise to, the perception 

 of white and black and all shades between — i. e., grays. 

 At that time only white and shades, but not colors, were 

 perceived. Next, some of this substance in the cones, 

 but not in the rods, was differentiated into two color- 

 substances — viz., yellow and blue — which, separately af- 

 fected, give rise to these two colors respectively, but 

 simultaneously affected, to white and shades. Lastly, 

 one of these two — viz., yellow — was again differentiated 

 into red and green ; but these by simultaneous affection 

 give rise still to yellow. 



COLOR-BLINDNESS. 



Many people seem to discriminate colors imperfectly, 

 but only because they do not observe carefully. They 

 see colors perfectly well, but have not learned to name 

 them. This is not color-blindness. 



What is Color-Blindness ? — The color-blind do 

 not see certain colors at all as colors, but only as shades. 

 To take one example: The commonest form of color- 

 blindness is that for the colors red and green. For such 

 a person the red berries and green leaves of a cherry 

 orchard, or the red carnations and the green lawn on 

 which they grow, look much alike, and neither of them 

 red or green, but gray. In a word, they look much as 

 a stereogram of the scene would look to an ordinary 

 person looking through the stereoscope ; for the iodized 

 plate is also blind for these colors. 



