506 
POPULAR SCIENCE REVIEW. 
agree that in the greatest number of cases it is not a disease, 
but rather a remarkable type of vision. It is known, however, 
that the peculiarity exists sometimes as a matter of degree, 
and that an abnormal sensation of colour may be received, but 
of so short a duration and corrected spontaneously as to be a 
source of little inconvenience, and even passes unnoticed. But 
as many important facts in connection with the subject have 
come to light, it is now made essential, and very properly so, 
for every driver or guard of the railway train to pass an 
examination as to his power of perceiving and distinguishing 
different coloured signals used on railways. Dr. Wilson goes 
further, and says : “ It admits of a question whether the 
demands of public safety would be best met by excluding 
colour from railway and ship signals, or by excluding the 
colour-blind from the office of signalmen. 55 Red and green 
lamps are employed as signals at sea, as well as on railways, 
and many appalling accidents, no doubt, have been occasioned 
by mistaking the colour exhibited both on sea and land. 
A mistake in colour may arise from the fact that the sensa- 
tion can only be prolonged for a very limited time. Thus, 
whenever any one looks fixedly at a bright object placed on a 
surface of a dark tint, and then closes his eyes, or transfers 
them suddenly to another ground of a lighter colour, he imme- 
diately perceives an image presenting a colour complementary 
to the one last observed. This arises, also, when the eyes 
have been fatigued by the prolonged observation of a coloured 
and very bright object, as a coloured light, and then suddenly 
turned to look at another object of a different colour ; or when 
the eyes are fatigued by overwork and hours of watching 1 . 
Many remarkable cases are on record where coloured vision 
has been suddenly produced. The particulars of a somewhat 
remarkable case lately excited some attention, and a medico- 
legal question of importance was raised. The sufferer, a 
corn-dealer, brought an action against a railway company for 
compensation, inasmuch as that after the accident every thing 
appeared yellow, and all qualities of flour, therefore, were 
alike in colour. The evidence chiefly depended upon the man’s 
own statement, as it appeared the eyes were carefully examined, 
and yet none of the medical witnesses could give any explana- 
tion as to the cause of the yellow vision. The jury, however, 
awarded £1,200 damages ; and as a certain amount of coloured 
vision is not unfrequently found to be associated with paralysis, 
it is not difficult to believe the retina may have been partially 
paralysed by the severe shock received in this railway 
collision. 
But whether we regard colour-blindness as only a curious 
physical phenomenon, simply a defect, or as a positively 
