290 Report of the Committee on Colour- Vision. 



Colour- blind- 

 ness caused 

 by disease. 



Statistics of 

 colour-blind- 

 ness. 



or grey seen in the spectrum would then be due to the white- 

 black sensation, as it alone is stimulated at that point.* (See 

 Note b.) 



The kinds of colour-blindness so far alluded to are the congenital 

 types, but there is another form of colour-blindness which is in- 

 duced by disease or injury. The former is apparently by far the 

 most common, and so far as we have ascertained, is incurable, 

 but the latter may be induced at any period of life, and in very 

 many cases is capable of improvement or cure. 



Colour-blindness induced by disease or injury exhibits dis 

 tinctive features of its own, which are not present in cases of 

 congenital colour-blindness. It is usually confined to the central 

 region of the retina, and the extent of the diseased area varies 

 largely. Defective form-vision is an invariable accompaniment, and 

 it can be usually diagnosed by the recognized tests. (For these 

 tests see Appendix VI.) In several cases induced by excessive use 

 of tobacco, as also in that induced by progressive atrophy of the 

 optic nerve, the Committee have found in examinations made with 

 the spectrum that the sensations of white and blue alone were 

 perceived in the central portions of the retina. The blue seen 

 corresponded with the blue region of the spectrum, and all other 

 colours were described as white. In other cases, a faint yellow 

 in the yellow portion of the spectrum was perceived together 

 with the blue and white, as in the first-named cases (see No. 5, 

 Plate I). That these sensations were rightly described is to be 

 assumed from the fact that these persons when in health have 

 normal vision, and also, that on healthy portions of the retina 

 all colours stimulate the normal sensations. (See Appendix C.) 



The earlier statistics of defective colour-sense must be dis- 

 missed as untrustworthy, having been arrived at by various, and 

 frequently by inaccurate methods of examination, and having, 

 on the whole, a marked tendency to error in the direction of 

 excess. The first on which reliance can be placed are probably 

 those of Dr. Joy Jeffries, of Boston, U.S.A., who personally 

 examined 19,183 male persons, mostly in educational institutions, 

 and who found among them 802 colour-blind, or 4-12 per cent. 

 Among 14,764 females, he found only 11 cases, or 0*0084 per 

 cent. In 1880, the Ophthalmological Society of London appointed 

 a Committee to inquire into the subject, and they found that 

 amongst 14,846 males, 617 or 4-16 per cent, were colour-blind. 

 Amougst 489 females, 0*4 per cent, were defective in colour- vision. 

 The report of this Committee is contained in the first volume 

 of the "Transactions" of the Society, and an extract from it 

 will be found in Appendix I. 



The Committee were furnished with some statistics regard- 

 ing colour-blindness in two Japanese regiments. Out of 1,200 

 men examined, 19 were red-blind, 10 green-blind, 12 incompletely 

 colour-blind, and 27 had weak colour-vision. This gives 3*4 



* Without deciding between these two theories, it has been found con- 

 venient to accept the terminology of the Young-Helmholtz theory. 



