574 



STUDIES IN ADVANCED PHYSIOLOGY. 



one color. The green-blind people see our red, although it 

 is yellow to them. In other words, their sense of sight is 

 aroused by what we call red. This is the second color. 



Fig. 179. DIAGRAMMATIC REPRESENTATION OF THE STRENGTHS OF THE THREE FUNDA- 



" MENTAL SENSATIONS IN THE DIFFERENT PARTS OF THE SPECTRUM. 



J, curve for color red; #, curve for green; 3, curve for blue. The red curve should 

 show a small added elevation at the violet end, since the stronger reappearance of the 

 red there causes with the blue the production of the violet. 



In red-blind persons the sensation of yellow is produced by 

 what we call green. Such a composition of two dichro- 

 matic eyes would therefore be (1) blue, (2) yellow where 

 we see green, (3) and yellow where we see red. Now, it 

 is just possible that for psychological reasons this primitive 

 yellow sensation has been divided into two separate sensa- 

 tions which we have learned to call red and green. One 

 can easily understand how by having two colors, even if 

 they are somewhat alike, side by side before the eye,, that 

 it would tend to make distinctions which would otherwise 

 go unnoticed. 



The normal eye is usually spoken of as a trichromatic 

 eye because of its ability to perceive three, different sensa- 

 tions. By the varying compositions of these different sen- 

 sations all the shades and tints, and intermediate colors 

 may easily be derived. When all three fibers in the eye 

 are stimulated in the proper proportion, white is the result. 

 This may be shown to be true by taking a card on which 

 the red, green and blue are put in the proper proportion 

 and then whirling it rapidly. The three colors melt to- 

 gether and the sensation of white results. The red and the 



