Report of the Committee on Colour-Vision. H87 



colour, even when directly comparing- them, is positive proof of 

 mistake, implying defective chromatic vision of the complete 

 colour-blind type. No doubt the form of chromatic defect which 

 we have called incomplete colour-blindness exists in several kinds 

 and degrees. This is not the place to further discuss our 

 experience on this point ; and, for the practical purpose we have 

 in view, it is not necessary. As we have explained, there are, 

 among this class, forms gradually approaching normal colour- 

 sense. How they are distinguished has been described. We 

 designated them as possessing feeble colour-sense. 



" It is, perhaps, not easy to detect this special form by any 

 other method, or even by our own; we therefore give the 

 following as a means of so doing. The only way of getting at it 

 is by determining at what distance the examined can distinguish 

 a small coloured surface. We have to do, in fact, with a feeble 

 colour-sense, which does not prevent the colours from being dis- 

 tinguished, but only renders it difficult. We may suppose, in com- 

 parison to the normal- that the feeble colour-sense is due either to 

 a weaker response to the stimulation of the colour-perceptive 

 organs of the retina, or else to a stimulation of a relatively 

 smaller number of these organs. In either case this method would 

 give us the same result, judging from our experience in testing 

 the eccentric portions of the field of vision with the perimeter. 



" The method we here speak of shows us also the effect of . 

 habit and practice on the colour-perception, and it is worth while 

 to dwell on this point. It not unfrequently happens that a person 

 who by test No. I has been noted 'incomplete colour-blind,' 

 after they know of their mistake and have practised themselves 

 in distinguishing colours, will so comport themselves at a second 

 trial that we have to simply mark them as of ' feeble colour- 

 sense.' This fact might support Dr. Favre's idea that defective 

 chromatic vision may be improved. This possibility, however, 

 does not militate against our hypothesis from the theory, as to 

 the nature of feeble colour-sense. It does not change our 

 standpoint in the question. The same will sometimes happen 

 with test No. II, and it is explainable by what we have said ; 

 uamely, that, between the complete lack of chromatic sense and 

 the incomplete, there is a series of gradations, and that in such 

 cases practice would affect the result of examinations. 



" All the examples given prove that many seeming trifles and 

 stratagems are of value in making the examination — amongst 

 others the keeping the sample a little way off from the heap of 

 worsteds, as also the removal of everything which can cause the 

 examined doubt and uncertainty. We must not, therefore, let 

 them do what many want to do ; namely, hold a number of the 

 worsteds in the hand at once. We must make the person being 

 examined place each skein, as he takes it up, either with the 

 sample or else back on the heap. Many who are not clear 

 whether the skein is like the sample or not, instinctively put 

 the shades most resembling the test sample at the side of the 



