COLOUR-BLINDNESS*. 
507 
abnormal condition in some one or more of the structures of the 
eye, it may be truly 'said we know so little concerning its true 
nature, that I need offer no apology for the few remarks I 
am about to add upon it. As I have often met with it asso- 
ciated with actual disease, and since by the invention of the 
ophthalmoscope we are now enabled to observe many very 
curious changes in the internal eye before unrecognized, it is 
not improbable by its aid we may ultimately discover some 
structural differences in the eyes of the colour-blind. And if 
the proposition be well founded that the colour of the internal 
membranes of the eye must affect its perception of colours, 
then the choroid, which is the most fully coloured of the tunics, 
and the one most liable to vary in extent and depth of coloration, 
must have a very important influence on colour- vision. Now, 
in the few cases that I have had the opportunity of examining, 
I noticed a considerable difference both in the quantity of 
pigmental colouring- matter, in the size of the vessels, and in 
the amount of blood circulating in the eye. This will be seen 
by any one not conversant with these matters, upon comparing 
the size, and perfection of the vessels in the otherwise sound 
eye represented in figure 1 with that of figure 2, a drawing- 
made from an eye in a state of disease, the person having also 
been colour-blind prior to the loss of sight. This, however, I 
am ready to admit, may prove to be the exceptional and not 
the general condition of the eyes in the colour-blind ; further 
investigations alone will settle this point. The seat or cause 
of the defect probably lies altogether beyond our reach ; but 
whatever we can learn concerning it is certain to be of service 
in determining the extent to which we may hope to cure or 
alleviate this affection of sight. 
The first case of colour-blindness that fell under my notice 
was that of my late talented friend, Mr. Angus Reach, whose 
untimely death has been so much and so justly lamented. He 
was incapable of distinguishing green, and only partially so 
red. With him both were nearly the same. The former would 
sometimes appear more of a pink than even red. He had 
altogether but a very poor conception of the primary colours. 
This I detected on one occasion when endeavouring to demon- 
strate the gradation of beautiful colours displayed by some 
objects made to depolarize light when placed on the stage of 
my microscope. After a long endeavour to convince him of 
the fact, as he could see nothing wonderful in it, I discovered 
that he was unable to name the colours correctly; and he 
then told me he had always been indifferent about them. To 
prevent error he had been accustomed always to avoid describ- 
ing them, except in relatively as light and shadow, or black 
and white. He remarked of the vin-orclinaire of France, that 
