RESEARCHES BASED UPON THE THEORY 



243 



slit must be moved towards the red, if a partial protanope towards 

 the green. 



There is a considerable band of the spectrum over which the slit 

 may be moved without vitiating the approximate dichromat's match, 

 but Watson 1 has pointed out that the match which satisfies the 

 normal person is always one limit of the band, though the band lies 

 sometimes on one side and sometimes on the other of this position. 

 There is at present no explanation of this fact. We shall find that the 



40 



30 



20 



10 



64 62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 



I I 1 I I I I I I I I I I I I I I 



7000 6500 6000 55K 



I I 



Fig. 72. Foveal luminosity curve of a deuteranope with excessive macular 



pigmentation. (Watson.) 



anomalous trichromat whose peculiarity is due to a shift of one of the 

 sensation curves makes a much more accurate setting by this method. 



IV. ANOMALOUS TEICHROMATIC VISION 



Shift of a Sensation Curve 



Abney and Watson 2 have published an exhaustive account of a case 

 of anomalous trichromatic vision in which the green sensation curve is 

 of normal shape and size but is displaced towards the red end of the 



1 Proc. Pay. Soc. Land. May 28, 1914. 2 Ibid. A. LXXXIX, 232 ; 1913. 



162 



