BY JOHN THOMSON, M.B. 



41 



authorities on the subject and finding no reference whatever to 

 a blue theory was beginning to congratulate myself, when 

 opening an old tome " that had long lain hid " I discovered that 

 Dalton had suggested that the red rays in his case were absorbed 

 by the vitreous humour which might have a blue colour or by 

 the retina itself having a blue tint. An examination of Dalton's 

 eyes was made after death, "but no blue vitreous humour, nor 

 blue retina was there, thus affording a refutation of both these 

 conjectures." 



I think the blue theory might be revived ; it is about aa 

 good as any at present ; and it might be worked in, in connec- 

 tion with a cyanic depravity of the visual purple. 



Cases of colour-blindness are also classified as Congenital 

 and Acquired. 



Congenital. — I believe those in my table are all congenital 

 and were in no way induced or aggravated by habit or disease. 

 Whether they were hereditary it ia impossible to say. Eighteen 

 (18) of the men were certainly unaware of any defect until after 

 examination and all declared they never heard of colour- 

 blindness among their relatives. The other two (2) knew of 

 their abnormality, but did not regard this as hereditary, Yet in' 

 the case of examinee 20, a solicitor, it is very distinctly so. A 

 nephew of his, a bright lad of 11, is colom -blind and in an 

 astonishing way followed the mistakes of the maternal uncle ; 

 and further enquiry elicited the fact that defective colour per- 

 ception is very distinctly hereditary in this well-known Brisbane 

 family, for of thirteen (13) males appearing in five (5) branches 

 during three (8) generations, six (6) are known to be colour- 

 blind, with in every instance the transmission, as to be expected,, 

 through the mothers, all of whom are said to enjoy normal 

 colour sight. 



HEREDITY OF COLOUE-BLINDNESS. 



Youngest 



of 13 



■F M 



F M M M M F F 



fMffMf ffM 



(The black letters M indicate the colour-blind.) 



