396 STUDIES IN SPECIAL SENSE PHYSIOLOGY 



Amounts of Red (Lithium Line) required to match a Standard Yellow 

 (Sodium Line) by II Protanopes and 9 Deuteranopes (v. Kries). 



Ratio is 5 : 1 (Approx.). 



which have been most studied are known as Protanopes and 

 Deuteranopes. Their special characters will be described briefly. 



Experimentally, we proceed as in the examination of normal 

 colour vision. A certain red and a certain blue are chosen ; the 

 whole spectrum matched and expressed in terms of the standard 

 lights. The tables and diagram (p. 395) embody the results 

 obtained by J. v. Kries ( 14 ). 



An examination of the curves shows that the cases fall into 

 two groups in respect of red values. The four sets of blue values, 

 on the other hand, are not very dissimilar ; in fact, remembering 

 that the physical differences of macular absorption would be most 

 influential in that region of the spectrum where the blue values 

 agree worst, we may regard the similarity as fairly close. 



Referring to the tables, we see that for matching spectral 

 lights of wave length greater than 530 /UL/J. no blue at all is 

 necessary, so that the forms of the red curves beyond this point 

 are especially instructive. In one group the curve rises fairly 

 sharply to a maximum in the neighbourhood of 571 /x/x, and then 

 falls sharply, suggesting a relatively low stimulus value for long- 

 waved light ; in the other group the rise is more gradual, attaining 

 a maximum at 603 nn, while the curve does not fall to so low 

 a point at the red end. 



1 One subject. 



