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Luminosity Values of two Case* of Total Colour-llimlness (Abney). 

 (No. 40 in Abney 's scale is close to the E line.) 



As we have already seen that direct evidence points to dark 

 adaptation being chiefly an affair of the extra-foveal part of the 

 retina, it is reasonable to suppose that, in the totally colour-blind, 

 the fovea centralis is relatively insensitive. It has indeed been 

 asserted that a central scotoma, or totally insensitive area, is 

 found in these cases, and much dispute has arisen on this point. 

 Summarising the results of examination, we find that, out of 

 eighteen cases investigated (Grunert l6 ), in seven an absolute or 

 relative central or para-central scotoma was definitely made out ; 

 in the other eleven this was absent. The importance of a central 

 scotoma has been greatly over-estimated for theoretical reasons, 

 as we shall see later. In most cases, very imperfect fixation or 

 actual nystagmus was observed. On reviewing the facts, it will, 

 I think, be admitted that the agreement in type between the vision 

 of the totally colour-blind and that of the normal " dark " eye 



