KANSAS ACADEMY OF SCIENCE. 



croscopic elements present, the special function of which we do not as yet 

 know. Moreover, this is not the most essential part in Young's hypothesis. 

 That seems to me to be the presenting of color sensations as composed of 

 three wholly independent actions in the nerve substance. It is not abso- 

 lutely necessary to suppose separate nerve fibers for these separate nerve sen- 

 sations. The same value of Young's hypothesis in this explanation is shown ^ 

 if we suppose that in each individual fiber three difierent and independent 

 actions may take place. Since, however, the form of the hypothesis, as 

 originally proposed by Young, is capable of a more definite presentation and 

 expression than such a modification of it would allow, we will in view of its 

 description retain the original and plainer form. Moreover, the physical 

 phenomena of nerve stimulation, namely, the electro-motor, are not marked 

 in the sensitive nerves and motor nerves by such a variation in action as 

 would necessarily be the case if each nerve fiber transmitted all color sensa- 

 tions. By Young's hypothesis we may apply to the optic nerve the concep- 

 tion of the mechanism of stimulation and conduction which we have derived 

 from the study of the phenomena of the motor nerves. This we could not 

 do, if we must admit that each optic nerve fiber is to have three qualitatively 

 difierent conditions of stimulation, without mutual interference. Young's 

 hypothesis is only a more special carrying-out of the doctrine of the specific 

 energies of the senses. As the sense of touch and the sense of sight in the 

 eye have evidently separate nerve fibers, so is the same claimed for the sen- 

 sation of the several base colors. The choice of the base colors is somewhat 

 arbitrary. Any three colors could have been chosen whose combination pro- 

 duces white light. So far as I see, at present, there is no other way of deter- 

 mining the base colors than by the examination of the color-blind." (JeflTries 

 Op. Cit., page 28.) 



In support of the Young-Helmholtz theory, its advocates oflPer these addi- 

 tional physiological facts: "Around the point of best vision, in the center of 

 the retina, is a zone, where we perceive all of the three so-called base colors — 

 red, green and violet. Outside of this is another zone, in which we have a 

 perception of only two colors, namely, green and violet; and again, beyond 

 this, and more externally on the retina, only blue or violet is perceived." 

 The advocates of the Young-Helmholtz hypothesis hold, therefore, to three 

 kinds of color-blindness — red blindness, green blindness and violet blindness. 

 For the present we dismiss the Young-Helmholtz theory, and take up that of 

 Prof Hering, of Prague. I copy from the American Journal of Medical 

 Sciences Prof. Hering's theory, as stated by Prof. Mauthner: 



"According to this theory, vision is produced by the action of light on 

 three separate and distinct chemical substances, which he calls the black- 

 white, the red-green and the blue-yellow. Sight acts on these substances by 

 assimilation and dissimilation. Dissimilation of the black-white substance 

 produces the sensation of white, its assimilation black. As regards the red- 

 green and blue-yellow substances, Hering is undecided as to the D and A 

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