528 THE HUMAN BODY. 



suggest two of the above, and maybe described as mixtures 

 of them; but they themselves stand out as fundamental color 

 sensations. Moreover, it follows from the above, that more 

 than two simple colored sensations are never combined in 

 a compound color sensation. 



Since red always excludes green, and yellow blue, we may 

 call them anti-colors (the complementary colors of Young's 

 theory), and are led to suspect that in the visual organ there 

 must occur, in the production of each, processes which 

 prevent the simultaneous production of the other, since 

 tnere is no a priori reason in the nature of things why 

 we should not see red and green simultaneously, as well as 

 red and yellow. Along with our color sensations there is 

 always some colorless from the black-white series; which 

 we recognize in speaking of lighter and darker shades of 

 the same color. 



Hering assumes, then, in the retina or some part of the 

 nervous visual apparatus, three substances answering to the 

 black-white, red-green, and yellow-blue sensational series, 

 the construction of each substance being attended with 

 one sensation of its pair, and its destruction with the other. 

 Thus, when construction of the black-white substance ex- 

 ceeds destruction, we get a blackish-gray sensation; when 

 the processes are equal the neutral gray; when destruction 

 exceeds construction a light-gray, and so on. In the 

 other color series similar things would occur; when con- 

 struction of red-green substance exceeded destruction 

 in any point of the retina we would get, say, a red feeling; 

 if so, then excess of -destruction would give green sensa- 

 tion. The intensity of any given simple sensation would 

 depend on the ratio of the difference between the construc- 

 tion and destruction of the corresponding substance, to the 

 sum of all the constructions and destructions of visual sub- 

 stances going on in that part of the visual apparatus. A 

 little thought will show that this can hardly be reconciled 

 with the results expressed in Fechner's law. The intensity of 

 a mixed color sensation would be the sum of the intensities 

 of its factors, and its tint and shade dependent on the rela- 

 tive proportion of these factors. When the construction 



