334 Report of the Committee on Colour-Vision. 



also for some optical reasons. In my testing lantern I have a 

 diaphragm with holes of different sizes, representing the regular 

 railway lights at different distances, with red and green glass 

 supplied by one of the Companies, and in addition a number of 

 bits of smoked glass. I often, but not always, succeeded in 

 getting the persons tested to confuse red and green, and also 

 white smoked light with coloured lights. The persons tested 

 should stand at a distance of 12 feet, and I vary the size 

 of the hole so as to represent a railway signal at different dis- 

 tances. Some time ago my colleague, Mr. Lawford, examined 

 an engine driver from the South Western Eailway, who came to 

 St. Thomas's Hospital because he had been rejected that morning 

 on account of colour-blindness, although he had been two years 

 previously tested and passed. His eyes were perfect but colour- 

 blind. With Holmgren's first series he matched green and red ; 

 and with the next series he confused greens and greys. He was 

 tried with the lamp, and then confused red and green in both 

 large and small dots, making more mistakes with green than 

 with red glass. Such a man, if he were very much on the 

 watch, might go on for many years with safety. He said 

 he never experienced any difficulty in telling the colours of 

 the signals because the red "glistened." I had a somewhat 

 similar case with a medical student who had been at sea. In 

 trying him with one of Stilling's tests, consisting of coloured 

 letters on a black ground, I found he could not see green on 

 black. I asked him if he could tell lights at sea, and he said, 

 " Yes, quite easily ; there is the red light and the black light." 

 I lately saw a man who had been a stoker on the Great Eastern 

 Kailway for a number of years and now wanted to pass as a 

 driver ; but on being tested was rejected as colour-blind. He 

 did not believe himself to be so, and came to Moorfields Hospital 

 for a certificate that his colour-vision was perfect. He proved, 

 however, to be an ordinary red-green blind. On the other hand, 

 we have had men appealing to us there because they had been 

 rejected who really saw colours quite well. 



Question — That probably occurred through using the naming 

 tests ? — Yes, I suppose so. 



Question — Does night-blindness throw an} 7 light on the question 

 of colour vision ? — I do not think so. Patients who have night- 

 blindness are certainly not colour-blind. In such cases I think 

 all colours disappear equally, together with form, but I cannot 

 speak with any authority on this point. A very night-blind 

 person would be deficient in the day also. Temporary night- 

 blindness is due to some want of nutrition of the retina, and is 

 often associated with scurvy. It is now a rare disease in this 

 country. The ordinary varieties of night-blindness are due to 

 disease of the retina. 



Question — Does this failure (the permanent night-blindness 

 due to disease) come on in middle life ? — It varies ; some are born 

 with the disease which causes it, and with others the disease 



