now \VK SKE. 1 , / 



tliouj^lit it inipossiMc thnt tlif iitiiiii -lumld l>f aide t<» re- 

 ceive or the optic iicivc should caiiy so man}' .sepanitc and 

 distinct impressions to the hrain. He, therefore, assnnied 

 that there were in the retina three iieive lihres which were 

 affected principally l»y the wave lengths ot' ether i'ej)rescnting 

 red, ureen, and violet. Thesi' lihres we will call the wd 

 lihre, tiie ••reen libre, and the violet tibre. When all of 

 these fibres are afieeted in eijual proportion the sensation 

 jirodueed is wliite, the absence of all sensation is Idack. 

 When the red tiljre is aftectctf we have a sensation of red; 

 when tlje fjiven Hl)re is affected the sensation is green; when 

 the red and green fibres are afieeted together the sensation 

 is yellow: and so on for all the colors with their coinbina- 

 tions and shades. Xow this is all very sirjiple and plausi- 

 ble. It is true no one has ever seen the fibres, but, so much 

 has t(» he taken for gi-anted in this department of scientific 

 investigation, that this point might readily he conceded if 

 there were no other obstacles in theway of an acceptance 

 of the theory. Nearly all the })henomena of colored vision 

 can be accounted for on this hypothesis if we so modify it 

 as to allow of some action on both the green and violet 

 fibres by the red rays, and some action on the green by the 

 red and violet, and on the violet bv the red and srrcen- For 

 myself, this necessary admission destroys the simplicity and 

 l)cauty of the hypothesis, for T hold that tlie phenomena of 

 vision, when thoroughly understood, will be found to be ex- 

 tremely simple in their character and in keeping with the 

 kno\Tn laws of light and its action on simple bodies. 



But the great and insurmountable objection to the hypoth- 

 esis is that it cannot account in a satisfactory manner for 

 all the phenomena of color-blindness. An acceptable theory 

 in regard to the function of an organ in liealth must account 

 al.^^o for all the derangements of that function. 



Without entering into any details, it may be hrieHy stated 

 that there are some phenomena presented by the color-blind, 

 which cannot be satisfactorily explained by the Young- 

 Helmholtz hypothesis. Physiologists are, therefore, becom- 

 ing dissatisfied with it. an<l are seeking for one which shall 

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