REVIEWS — RESEARCHES ON COLOUR-BLINDNESS. 153 



tvreen the experimenter and the colour-blind subject. "We cannot do 

 better than give Dr. Wilson's own words on this point. 



" All cases of colour-blindness agree in this ; that to the extent of 

 its occurrence in any one, it implies a condition of vision, in reference 

 to which there is not a common experience, and therefore cannot be a 

 common language between those conscious of colour and those un- 

 conscious of it. The information, accordingly, which they can con- 

 vey to each other is almost solely of a negative kind. We cannot, 

 for example, give to one who never saw green a positive conception 

 of what we understand by it; we can at best make him aware that 

 it is none of the colours he does see. And he, on his part, cannot 

 make us understand what positive impression green makes upon his 

 eye, although he may satisfy us that it is something different from 

 that which blue or yellow makes." 



Such considerations as these require not only the utmost skill and 

 care in the investigator, but render a classification of the observed 

 phenomena extremely difficult, if not, in the present state of our 

 knowledge, impossible. Accordingly we find in the present treatise 

 even the small attempts at classification made by preceding writers 

 overthrown, and the classification with which Dr. Wilson himself sets 

 out is abandoned before the close ; there really seems no other state- 

 ment at present to be made than that the varieties of colour-blindness 

 are infinite in number and insensible in gradation. 



With regard to the statistics of this defect, Dr. Wilson's researches 

 present us with the startling result that nearly one in eighteen of the 

 whole population is more or less colour-blind, a conclusion drawn from 

 an examination of 1154 cases taken indiscriminately and comprising 

 a corps of soldiers, of the Edinburgh police, and the students of the 

 University. There is also no doubt that the defect is hereditary, and 

 runs in families ; and that, though generally coexistent with infancy, 

 it may be temporarily induced by certain diseases, and even per- 

 manently by cerebral injury. A strange exemption is exhibited in 

 the case of females, among whom Dr. Wilson has been able to furnish 

 only two or three instances of colour-blindness. "Its occurrence," 

 says our author, with small show of gallantry, " probably appears 

 more rare than it is, and chiefly because the value set by women upon 

 a nice appreciation of colours, makes them reluctant to confess that 

 they are not quick or accurate in judging of them." Long ago Grail 

 announced that the phrenological organ of colour was more develop- 

 ed among females than males, a fact deemed to bo contrary to ex- 

 perience since no woman has ever been a great painter, and their 

 perception of harmony of colour has always been considered weulc, 



