334 



THE SPECIAL SENSES. 



It will be observed that the theory gives an independent ob- 

 jective cause for the sensations of white, black, and yellow, and in 

 this respect satisfies the objections made on this score to the Young- 

 Helmholtz theory. It fits better, also, the facts of partial and total 

 color blindness. In the latter condition one may assume, in terms of 

 this theory, that only the white-black substance is present, while 

 red and green blindness both of them, it will be recalled, really 

 forms of red-green blindness are explained on the view that in such 

 persons the red-green substance is deficient or lacking. On this 

 theory, complementary colors red and blue-green, yellow and 

 blue are, in reality, antagonistic colors. When thrown on the 

 retina simultaneously their effects neutralize each other, and there 



Fig. 145. Schema to illustrate the Hering theory of color vision. (Foster.) The 

 curves indicate the relative intensities of stimulation of the three color substances by dif- 

 ferent parts of the spectrum. Ordinates above the axis, X-X, indicate catabolic changes 

 (disassimilation), those below anabolic changes (assimilation). Curve a represents the 

 conditions for the black-white substance. It is stimulated by all the rays of the visible 

 spectrum with maximum intensity in the yellow. Curve c represents the red-green sub- 

 stance, the longer wave lengths causing disassunilation (red) , the shorter ones assimilation 

 (green). Curve b gives the conditions for the yellow-blue substance. 



remains over only the disassimilatory effect on the white substance 

 which is exerted by all the visible rays. The effect of the various 

 visible rays of the spectrum on the three photochemical substances 

 is illustrated by the chart given in Fig. 145. Ordinates above the 

 abscissa representing disassimilatory effects; those below, assimi- 

 latory. 



III. The Franklin Theory of Color Vision (Molecular Dissocia- 

 tion Theory). This theory, proposed by Mrs. C. L. Franklin,* takes 

 into account the fact of a gradual evolution of the color sense of the 

 retina from a primitive condition of colorless vision such as still 

 exists in the periphery of the retina and in the eyes of the totally 



* Franklin, "Zeitschrift f. Psychologie und Phys. d. Sinnesorgane," 1892, 

 iv; also "Mind," 2, 473, 1893, and " Psychological'Review," 1894, 1896, 1899. 



