42 COLOUR-SIGHT AND COLOUR-BLINDNESS 



Congenital cases are permanent, are not amenable to any 

 treatment, and educational training has no efifect. 



Acquired. — I have not detected a case of acquired colour- 

 blindness. It is stated " to commence as a rule in the centre of 

 the field and is an almost pathognomonic sign of what is com- 

 monly called ' tdxic amhlt/opia,' that is to say, of a neuritis which 

 is limited (at the beginning) to the macular fasciculus of retinal 

 fibres, and caused by the excessive use (excess either absolute or 

 relative to the idiosyncrasy of the patient) of tobacco, 

 of alcohol and possibly of other agents, either singly or in 

 combination." Mr. Priestly Smith has pointed out " that as a 

 rule the disease is not produced by tobacco alone but by some 

 cause of depression acting upon a large consumer, such as 

 shipwreck and its attendant hardships upon a sailor, or financial 

 anxieties upon a great smoker who is engaged in trade." 



As the disturbed retinal area may be limited, the colour of 

 a large object may be easily perceived by the unaffected areas, 

 while that of a small one, falling within the diseased limits, 

 cannot be seen. 



Dangers from Colour-Blindness. 



That there are colour-blind people, people who cannot see 

 red or green or confuse the two is undoubted ; and it would be 

 a grave danger to travellers by sea or land if these defective- 

 sighted individuals were in charge of our ships or our trains. 



The side lights of all vessels of all countries are green 

 (blue-green) and red (rich ruby). Green for the starboard, or 

 right side of the ship ; red for the port, or left. 



On land, on the railways, green is the safety light ; red, 



the danger signal. 



In the Report of the Committee on Colour Vision, presented 

 to both Houses of the Imperial Parliament in June, 1892, it is 

 said " The direct evidence before them (the Committee) is not 

 sufficient to cause them to say that accidents, either by sea or 

 land, have conclusively been traced to defective colour vision ; yet 

 this by no means disproves the high probability that accidents 

 have really occurred from such defects." And the safe<;y cf the 

 travelling public is made secure so far as defective colour per- 

 ception is concerned by insisting upon the employment of those 

 only who possess a normal colour sense. And this of course 

 necessitates careful and scientific examination and selection. 



