A Quantum Theory of Colour Vision. 



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that we can regard them as functionally reduced to three nerves, the liminal 

 excitatory stimuli of which are in the ratio of 2:3:4: units of energy, and 

 which discharge into the visual centre of the brain quantities of energy in 

 the same ratio, that is, 2 : 3 and 4 pliotons ? 



The latter assumption certainly facilitates the conception of their manner 

 of functioning. If such is the real state of the case, the cone of the 

 deuterauope possesses but two nerves or nerve-groups, having excitatory 

 stimulus values in the proportion 2 : 4. His green-blindness follows at once, 

 for he does not possess any apparatus competent to discharge an intermediate 

 stimulus — i.e., one of the value of thi-ee photons. So also in the case of the 

 proteranope ; the missing apparatus is that which discharges two photons in 

 the cerebral cortex, i.e., which creates the red sensation. 



It seems, however, possible that nine unco-ordinated libres offer an equally 

 good explanation of the whole matter. For consider the development of 

 colour- vision in the young child. The three fundamental sensations have 

 never before been experienced, but they are latent, and will in due course 

 arise as part of his consciousness. In the normal eye, white light — which is 

 by far the most abundant and prevalent light in Xature — excites all of the 

 three latent sensations, and in an equal degree. Later, when coloured 

 objects attract the attention of the child, the latent sensations begin to 

 assert themselves separately under the specific stimulus of each colour. 

 Two-fibre stimuli excite the latent red sensation, and so on. 



In the case of the green-blind there are only six fibres present. He may 

 possess as an infant all the three sensations latent. However, the ubiquitous 

 white light activates six fibres only. !N"ow these must be two- and four-fibre 

 stimuH, for, admitting that the three quanta possess an equal chance in the 

 first instance of capturing their appropriate number of fibres, these quanta 

 have to compete with two-fibre and four-fibre quanta, and the allocation two 

 ■and four alone activates all the fibres, a state which is characteristic of white 

 light and must arise under photopic conditions. His two-fibre sensation and 

 his four-fibre sensation are, therefore, developed, while a latent three-fibre 

 sensation will become atrophied. Three-fibre (green) quanta will, indeed, as 

 in the normal eye, activate much red sensation and some blue sensation fibre- 

 groups. Otherwise he fails to get any benefit from the quanta. In the case 

 of the red-blind the same causes are operative to retard or annul the educa- 

 tion of the red sensation. The anatomical question at issue might possibly 

 yield to histological research. 



(14) In order to understand in what manner all the varied hues of the 

 spectrum arise out of the present hypothesis, consider a specific case, say, 

 yellow sensation. Yellow sensation is felt when 2 <^ -f- 3 are simultaneously 



