34 KANSAS ACADEMY OF SCIENCE. 



colors. But if we take the red and blue as the D colors, the D of the red- 

 green substance would produce red, its A green, and the D of the blue- 

 yellow substance would call forth blue, and its regeneration yellow. All the 

 rays of the solar spectrum act in a dissimilating manner on the black-white 

 substance: that is, they produce the sensation of white, but in different de- 

 grees, the yellow acting most powerfully, the others decreasing in power to- 

 ward the two ends of the spectrum. On the blue-yellow and red-green 

 substances there are certain rays which act in a dissimilating manner, some 

 in an assimilating manner, and some not at all. If the A and D of the 

 black-white substance are of equal intensity, the result is gray. If the A 

 and D of the red-green and blue-yellow substances are equal, the result is 

 negative as to color, and there only remains the dissimilating action of those 

 colors on the black-white substance, that is white. (Amer. Jour. Med. Sci., 

 Oct. 1880, page 532.1 According to Hering, therefore, the so-called com- 

 plementary colors are not complementary, but on the contrary, antago- 

 nistic. By their mixture they do not produce white, but being neutralized 

 they allow the white sensation, which they all produce, in a greater or less 

 degree, to come prominently forward. The phenomena of color-blindness, 

 as based on this theory, are as follows : In the achromatrope all the rays of 

 whatever refrangibility, acting in a dissimilating manner, white or its shade, 

 gray, is produced. In the dichromatrope, besides the black-white there is 

 only one other substance that can be acted on by the different color rays. If 

 this is the blue-yellow (constituting red-green blindness), the red-yellow and 

 green light act in a dissimilating manner, and the blue in an assimilating 

 manner. The most strongly dissimilating color is yellow; the others are 

 varying — sometimes the red is stronger than the green, and vice versa. To 

 some of the light-waves at the red end of the spectrum, the colored as well 

 as the black-white substance is insensible. In the same way, in case of blue- 

 yellow blindness, where there is only the red-green substance, in addition to 

 the black-white substance, the red-yellow and blue lights act dissimilatingly, 

 and the green assimilatingly. The D color is red, the A color green, and 

 there are certain color rays at the blue end of the spectrum which do not act 

 on either one of the substances. In this case we should have a shortening 

 of the spectrum at the blue end ; as in the former case, there would be a 

 shortening of the red end. As an A and D of equal intensity of any one- 

 color substance would result in a total abolition of both colors, so where we 

 have such an action in the case of a dichromatrope, there would be no color 

 perception at all, but only the sensation produced by the action of light on 

 the black-white substance, that is, gray. It is on this account that certain 

 shades of color appear as gray to the dicromatrope. Purple and bluish 

 green are the colors which most dichroraatropes confound with gray ; but as 

 the dissirailative power of any is not the same in all dichromatropes, we 

 should not expect to find, according to this theory, the same shades of those 

 colors to be invariably confounded with gray. To one, a certain shade would 



