BELL. — TYPES OF ABNORMAL COLOR VISION. 1 1 



low degree of color sense with particular weakness of red sensation. 

 (24) corresponds with a description by Burch (Physiological Optics, 

 p. 119, of a case of predominant green sensation so marked that vision 

 was almost monochromatic, which makes it probable that the red and 

 blue sensations were weakened. Indeed it seems likely that great 

 exaggeration of one sensation may be associated with weakness of one 

 or both the remaining sensations. (25) seems to agree well with a case 

 cited by Edridge-Green (Colour Blindness, p. 203) as examined by Sir 

 Win. Ramsay. In this case there was remarkable exaggeration of 

 the blue, and degradation of the other sensations, so that vision was 

 almost monochromatic. 



All the color abnormalities here noted are such as belong to the 

 simple trichromatic theory assuming that the several color sensation 

 curves retain their shapes and their normal position in the spectrum, 

 varying only in area. So little is known of the mechanism of color 

 vision that one cannot even predicate whether shifts and changes of 

 shape are or are not likely to take place. Indeed these could hardly 

 be differentiated from other variations except they chanced to be very 

 marked indeed. Even the interesting case described by Abney and 

 Watson (Proc. Roy. Soc, 89, A, p. 232) as showing a shift of the 

 green sensation toward the red should be tested by the junction and 

 end points and by Burch's fatigue method before forming a final judg- 

 ment. 



If this shifting, or a change of shape in the sensation curve should 

 prove real, still further classes of variants would be formed, but how- 

 ever that may be, the mere variations of sensation curve area which 

 are known to take place must give rise, assuming a certain relation 

 between them as normal, to the definite groups of color variants here 

 noted. 



Of the 26 abnormal types of congenital color vision in this list 16 

 are fairly represented in recorded cases. Seven of the remaining 10 

 are types having two sensations + and thus varying from a simple 

 deficit of the remaining sensation 'only in the degree of luminosity of 

 the other two. The best method of differentiation here seems to be 

 careful study of the end points, and fatigue tests. The remaining 

 three involve abnormal blue vision combined with abnormal green 

 vision, both of which separately seem to be relatively rare. Whether 

 they are so in fact is somewhat dubious since with the commoner tests 

 all the smaller variations in the blue are likely to be missed or merged 

 in variations of pigmentation or color in the lens, while certainly most 

 of the -{- G types are placed with the more familiar — R. In all the 



