58 



NATURE 



[May 15, 1890 



ing with the entrance of the optic nerve, so it was re- 

 "served for a still later generation to discover the existence 

 ■of so common a defect as colour-blindness. The first re- 

 •corded case was described to Dr. Priestley by Mr. 

 Huddart, in 1777, and was that of a man named Harris, 

 a shoemaker at Maryport in Cumberland, who had also 

 a colour-blind brother, a mariner. Soon afterwards, the 

 case of Dalton, the chemist, was fully described, and led 

 to the discovery of other examples of a similar kind. 

 The condition was still, however, looked upon as a very ex- 

 ceptional one ; insomuch that the name of " Daltonism" 

 was proposed for it, and is still generally used in France 

 as a synonym for colour-blindness. Such use is objec- 

 tionable, not only because it is undesirable thus to per- 

 petuate the memory of the physical infirmity of an 

 eminent philosopher, but also because Dalton was a red- 

 blind, so that the name could only be correctly applied 

 to his particular form of defect. 



Colour-blindness often escapes detection on account 

 of the use of colour-names by the colour-blind in the 

 same manner as that in which they hear them used by 

 other people. Children learn from the talk of those 

 around them, that it is proper to describe grass as green, 

 and bricks or cherries as red ; and they follow this usage, 

 although the difference may appear to them so slight that 

 their interpretation of either colour-name may be simply 

 as a lighter or darker shade of the other. When they 

 make mistakes, they are laughed at, and thought careless, 

 or to be merely using colour-names incorrectly ; and a 

 common result is that they rather avoid such names, and 

 shrink from committing themselves to statements about 

 colour. Dr. Joy Jefferies gives an interesting description 

 of the almost unconscious devices practised by the colour- 

 blind in this way. He says : — 



"The colour-blind, who are quick-witted enough to dis- 

 cover early that something is wrong with their vision by 

 thesmiles of their listeners when they mention this or that 

 object by colour, are equally quick-witted in avoiding so 

 doing. They have found that there are names of certain at- 

 tributes they cannot comprehend, and hence must let alone. 

 They learn, also, what we forget, that so many objects of 

 every-day life always have the same colour, as red tiles or 

 bricks, and the colour names of these they use with free- 

 dom ; whilst they often, even unconsciously, are cautious 

 not to name the colour of a new object till they have 

 heard it applied, after which it is a mere matter of 

 memory stimulated by a consciousness of defect. I have 

 often recalled to the colour-blind their own acts and 

 words, and surprised them by an exposure of the mental 

 jugglery they employed to escape detection, and of which 

 they were almost unaware, so much had it become matter 

 of habit. Another important point is, that as violet- 

 blindness is very rare, the vast majority of defective eyes 

 are red or gieen blind. These f ersons s^e vi( let and yel'ow 

 as the normal-eyed, and they naturally apply these 

 colour-nan' es correctly. When, therefore, they fail in 

 red or green, a casual observer attributes it to simple 

 carelessness — hence a very ready avoidance of detection., 

 It does not seem possible that anyone who sees so much 

 correctly, and whose ideas of colour so correspond with 

 our own, cannot be equally correct throughout, if they 

 will but take the pains to notice and learn." 



When the colour-blind are placed in positions which 

 compel them to select colours for themselves and others, 

 or when, as sometimes happens, they are not sensitive 

 with regard to their defect, but rather find amusement in 

 the astonishment which it produces among the colour- 

 seeing, the results which occasionally follow are apt to be 

 curious. They have often been rendered still more 

 curious, by having been theunconscious work of members 

 of the Society of Friends. Colour-blindness is a structural 

 peculiarity, constituting what may be called a variety of 

 the human race ; and, like other varieties, it is liable to be 

 handed down to posterity. Hence, if the variety occurs 



in a person belonging to a community which is small by 

 comparison with the nation, and among whose members 

 there is frequent inter-marriage, it has an increased prob- 

 ability of being reproduced ; and thus, while many of 

 the best known of the early examples of colour-blindness, 

 including that of Dalton himself, were furnished by the 

 Society of Friends, the examinations of large numbers 

 of scholars and others, conducted during the last few years, 

 have shown that, in this country, colour-blindness is more 

 common among Jews than among the general population. 

 The Jews have no peculiarities of costume ; but the 

 spectacle, which has more than once been witnessed, of a 

 venerable Quaker who had clothed himself in bright green 

 or in vivid scarlet, could scarcely fail to excite the derision 

 of the unreflecting. Time does not allow me to relate 

 the many errors of the colour-blind which have been 

 recorded ; but there is an instance of a clerk in a Govern- 

 ment office, whose duty it was to tick certain entries, in 

 relation to their subject-matter, with ink of one or of 

 another colour, and whose accuracy was dependent upon 

 the order in which his ink-bottles were ranged in front of 

 him. This order having been accidentally disturbed, great 

 confusion was produced by his mistakes, and it was a long 

 time before these were satisfactorily accounted for. An 

 official of the Prussian Post-Office, again, who was 

 accustomed to sell stamps of different values and colours, 

 was frequently wrong in his cash, his errors being as often 

 against himself as in his favour, so as to exclude any 

 suspicion of dishonesty. His seeming carelessness was 

 at last explained by the discovery of his colour-blindness, 

 and he was relieved of a duty which it was impossible for 

 him to discharge without falling into error. 



The colour-mistakes of former years were, however, of 

 little moment when compared with those now liable to be 

 committed by engine-drivers and mariners. The avoid- 

 ance of collisions at sea and on railways depends largely 

 on the power promptly to recognize the colours of signals ; 

 and the colours most available for signalling purposes are 

 red and green, or precisely those between which the 

 sufferers ixo\c\. the two most common forms of colour- 

 blindness are unable with any certainty to discriminate. 

 About thirteen years ago there was a serious railway 

 accident in Sweden, and, in the investigation subsequent 

 to this accident, there were some remarkable discrepan- 

 cies in the evidence given with regard to the colour of 

 the signals which had been displayed. Prof Holmgren, 

 of the University of Upsala, had his attention called to 

 this discrepancy, and he found, on further examination, 

 that the witness whose asseitions about the signals 

 differed from those of other people was actually colour- 

 blind. From this incident arose Prof Holmgren's great 

 interest in the subject, and he did not rest until he had 

 obtained the enactment of a law under which no one can 

 be taken into the employment of a Swedish railway until 

 his colour-vision has been tested, and has been found to 

 be sufficient for the duties he will be called upon to per- 

 form. The example thus set by Sweden has been fol- 

 lowed, more or less, by other countries, and especially, 

 thanks to the untiring labours of Dr. Joy Jeffries, of 

 Boston, by several of the United States ; while at the 

 same time much evidence has been collected to show the 

 connection between railway and marine accidents and 

 the defect. 



It has been found, by very extensive and carefully con- 

 ducted examinations of large bodies of men, soldiers, 

 policemen, the workers in great industrial establishments, 

 and so forth, as well as of children in many schools, that 

 colour-blindness exists in a noticeable degree, as I have 

 already said, in about four per cent, of the male indus- 

 trial population in civilized countries, and in about one 

 per thousand of females. Among the males of the more 

 highly educated classes, taking Eton boys as an ex- 

 ample, the colour-blind are only between two and three 

 per cent., and perhaps nearer to two than to three. 



