198 ON COLOUB-BLINDNESS. 



sets the limits of vision of children more completely than 

 has yet been attempted. 



Two cases of colonr-blindness have fallen under my notice, 

 and although it would be improper to rest a theory on such 

 a very limited basis, yet observations, so far as they go, sup- 

 port the explanation stated. 



The first case is that of a gentleman who could not name 

 any colour but blue. On being given an assortment of 

 coloured wafers to arrange, he first singled out all blue ones 

 and also a number of pink wafers, saying that these were all 

 blue. The others he arranged, without any reference to 

 colour, in an order which appeared to him to represent 

 difference of shade ; dark chocolate, red, and green being 

 placed indiscriminately in one class, orange and light green 

 wafers forming another, yellow and light grey a third, and 

 white the last. To all appearance these colours struck his 

 eye as more or less dark shades of grey. In monochromatic 

 sodium light he arranged the colours in the same way, and 

 said that to him they presented no change of . appearance. 

 He was incapable of distinguishing any colour in polarised 

 lifht, and indeed denied that there was any difference in 

 intensity of shade. Now to a normal eye, blue appears 

 darker. I.e., less illuminated than yellow; but of course it 

 is difficult to compare the relative shades of two wholly 

 different colours. This gentleman was able to perceive light 

 at the violet end of the spectrum where a normal eye could 

 see nothing; and his vision was much restricted at the red 

 end. Ho could see a solution of sulphate of quinine in gas- 

 light as coloured, and named it blue ; by an ordinary eye 

 the solution cannot be distinguished from water in artificial 

 light. 



The other case which I examined was a more usual one. 

 The subject was unable to distinguish green from red. It 



