Report of the Committee on Colour- Vision. 331 



retinal image falls on the undamaged part of the red-perceiving 

 field, or because, though the image falls on none but damaged 

 percipient elements, it occupies so many of them that a correct 

 sensation is the result. But if the red test be of from 5 to 20 mm. 

 diameter, the patient will call it variously "no colour," or 

 "brown," or "black," or later on, perhaps, "white;" finally, 

 after having recognised it correctly in the eccentric parts of the 

 field, he may continue to recognise it correctly, though as a 

 "paler" a "duller" red, even at the centre. If a light-green 

 spot be used as the test, it will commonly be called "white," 

 sometimes "grey," on the defective area. I think they never 

 call pure red yellow ; certainly not often. They more often call it 

 brown. 



Question — With reference to tobacco amblyopia, is there any 

 particular kind of tobacco you have found to cause it more 

 than others? — All strong tobaccos, especially " shag," cavendish, 

 and strong cigars. 



Question — Are cases sometimes caused by alcohol, or by 

 tobacco only? — There is a great difference of opinion as to 

 whether alcohol alone can produce this form of amblyopia, or 

 any form at all commonly. Some think it often causes central 

 amblyopia, though I have never seen a case where alcohol alone 

 had done so. There is abundant evidence that tobacco alone can 

 cause it in cases of teetotalers. We also know tobacco cases occur 

 in women smokers. A large number of carefully recorded facts 

 by various observers, bearing on the influence of alcohol and 

 many other points in relation to this so-called "toxic" amblyopia 

 will be found in the " Transactions of the Ophthalmological Society 

 of the United Kingdom," vol. vii, p. 36 (1887). 



Question — In cases of persons who are heavy smokers of 

 strong tobacco who get amblyopia, is it not usually some mental 

 depression such as would be caused by the loss of a wife or 

 child that causes the tobacco to take effect ? — Yes ; I have for 

 many years insisted strongly on the frequency with which the 

 onset of failure of sight in smokers has been preceded by 

 something which, directly or indirectly, has caused a lowering 

 of general vigour. It is comparatively seldom that when tobacco 

 amblyopia comes on the subject is in his usual vigour and health. 



Question — Do you think these cases of scotoma in railway 

 servants and others are not common enough to be worth con- 

 sideration? — They are not at all so rare as to be unimportant 

 from the point of view of signal reading, but the safeguard is 

 that they always suffer from defects of form-sense, and that 

 causes them so much inconvenience that they take advice for it. 

 Though they might now and then manage to carry on their signal- 

 ling duties for a time, such an event would be rare. 



Question — Do you find that people engaged in the open air 

 suffer less in this respect than those employed indoors, such as 

 clerks ? — I do not know that it affects any class particularly, 

 apart from depressing or exhausting causes. 



