BY JOHN THOMSON, M.B. 37 



II. — Partial Colour-Blindness. 



1. Complete Partial. Dyschromatopsia. 



In which one of the primaries (adopting the 

 trichromic theory) is totally awanting. 



a. Red blindness — complete. 



b. Green ,, ,, 



c. Violet ,, ,, 



2. Incomplete Partial. 



Where one or more of the three primaries is 

 defective or inferior in excitability. 



a. Red blindness — incomplete. 



h. Green ,, ,, 



c. Violet ,, ,, 



d. Feeble chromatic sense. 



This classification is purely arbitrary, far too exacting, and 

 signally fails to account for the overlapping cases which I have 

 seen and recorded but of which I am unable to determine the 

 exact defect. As one author puts it, " there is no such sharp 

 and absolute distinctions in any case as the hobby-riding colour 

 theorist sometimes avers." 



I have now examined for colour vision 1128 candidates for 

 employment in the Queensland Government Railways, but I am 

 sorry to admit that I have only exact records of the last 782, 

 and I discovered among these 18 colour blind individuals or 2*3 

 per cent., which is considerably under the usual returns of 4 or 

 6 per cent. 



In no case have I found a candidate with normal colour 

 vision in one eye and colour blindness in the other ; nor have I 

 met with a case of total colour-blindness except possibly one ; 

 nor a case of feeble chromatic sense. All my cases have been 

 well marked, as will be seen from the accompanying table — a 

 table which I believe to be unique. I have hunted in vain 

 through British literature for such a record. Odd and vague 

 statements are constantly to be met with referring to the 

 mistakes of the colour-blind, but this is the only table I am 

 aware of where are to be found, in minute and scientific detail, 

 the blunders of twenty (20) colour-blind individuals, tested on a 

 trichromic basis. This table gives the details of the examina- 

 tion of twenty (20) men who have been certified colour-blind — 

 two (2) of these were not railway men. 



The method of testing is by showing the examinee a skein 

 of coloured worsted — a test skein — and asking him to point out 



