A Quantum Theory of Colour Vision. 



225 



An interesting deduction from the present theory is that, under 

 conditions of increasing stimulation with any one colour, there should be 

 change of hue leading ultimately to white sensation. This is so because 

 if the supply of quanta is in excess of what will engage all available fibres 

 there will arise summation of stimuli, and finally the complete activation 

 of all nine fibres. The sensation of being dazzled then arises, and we feel 

 the white sensation, the more normal creation of which is due to simul- 

 taneous orderly excitation of two, three and four fibre groups. 



(11) The bearing of these views on colour-blindness is as follows : — 

 Following Dr. Parsons, I shall use the term deuteranope to denote the 

 green-blind dichiomate, and the term proteranope to denote the red-blind 

 dichromate. To make my remarks more intelligible, I reproduce here 

 (fig. 2) Konig's and Dieterici's curves.* 



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720 700 680 660 640 620 600 580 560 540 520 500 480 460 440 420 400 380 

 a B C D E h F G II 



Fig. 2. 



The red curve and the blue curve of the deuteranope are normal. We 

 have therefore no reason to suppose his colour interpretive mechanism 

 respecting red and green different from that of the normal retina. He 

 possesses a two-fibre sensation and a four-fibre sensation. He sees his 

 " white " light (grey) at a point on the spectrum, where at tlie intersection of 

 the two curves both colours stimulate equally. He must possess six fibres 

 leading from his cone, as compared with nine in the case of the normal eye. 



It is, I think, easy to understand that this number will not favour the 

 development of a green sensation. White light prevails above all other in 

 Nature, for white is the colour of sun-light. His receptive mechanism, 

 when fully activated by white light, can stimulate but two complete 



' Die Grundempfindungen,' Konig and Dieterici, Hamburg and Leipzig, 1892. 



