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Dr. F. W. Edridge-Green. [Nov. 15, 



The Relation between Teichromic Vision and Anomalous 

 Trichromatism. 



Anomalous trichromatism should be clearly defined as the condition in 

 which anomalous matches are made by a person who refuses to accept the 

 normal match. Much confusion exists on this point ; a person who agrees 

 with the normal equation cannot be regarded as an anomalous trichromat 

 even though he agrees at the same time with the anomalous matches. 

 This is only evidence of colour weakness, inasmuch as both equations are 

 regarded as satisfactory. There are many anomalous trichomats who are 

 not colour weak and there are many trichromics who make absolutely normal 

 equations. Trichromic vision in my classification is therefore not synonymous 

 with anomalous trichromatism. There are also persons who will make the 

 normal equation in one set of circumstances and anomalous equations in 

 another (14). There are also those who will make normal equations when 

 the red employed is A. 670 but will make an anomalous equation with a red 

 of larger wave-length, as for instance \ 690, putting twice as much red in 

 the mixture compared with the normal equation in similar circumstances (16). 

 Anomalous trichromatism when too much red is put in the mixed colour may 

 •correspond to defect in the perception of certain red rays, namely those 

 employed in the mixed colour. I have shown (5) that when there is 

 shortening or much defect in the perception of red the junctions of the other 

 colours are shifted towards the violet end of the spectrum. The yellow, 

 therefore, corresponding to the D line, is seen as a much redder colour than 

 the normal, and if we consider that the green is similar to the normal it is 

 obvious that more red will be put in the mixture than by the normal-sighted. 

 This shortening of the spectrum may be associated with normal vision in 

 other respects or with any degree of defective colour differentiation, that is to 

 say, it may be associated with dichromic, trichromic, tetrachromic, penta- 

 chromic, hexachromic or heptachromic vision. A similar condition is also 

 found for the violet end of the spectrum. It is obvious that a man, who has 

 shortening of the red end of the spectrum or defect in the perception of red, 

 is colour weak as far as red is concerned. Unless, however, he has defective 

 hue perception he may make no other error than that directly connected with 

 the defective perception of certain red rays. It is different with those who 

 make an anomalous match in which too much green is put in the mixed 

 •colour. As found by Eayleigh (6), Kollner (20), v. Kries(lO), Hagel(13), and 

 myself (14), a man may make an anomalous match without presenting any 

 other colour defect. I have found 25 per cent, of men to be more or less 

 colour weak, and it is, therefore not surprising that anomalous trichromatism 



