1892-93.] Dr William Pole on Colour-Blindness. 
115 
blind was on the average about 502 ’8 ; for a typical red-blind about 
Professor Stilling on Colour-Blind Vision, 1883. 
This author points out that the cliief element of variation is the 
variable sensitiveness of the patients to the influence of the long 
waved rays, and he divides them into three classes ; — 
(1) Those who have the normal sensibility for these rays, i.e., 
those who, though they do not see the normal colour, receive in tlie 
pseudo-colour about the normal degree of colour-giving power. 
[This is my case.] 
(2) Those whose sensitiveness in this way is less than the 
normal, so that although the whole of the rays impress them, it is 
with less than the normal power. 
(3) Those who have a shortened spectrum at the red end ; and to 
whom, therefore, some portions of the long-waved rays are 
absolutely powerless. 
These grades, however, run into each other. 
The author also refers to variations in the effect of the green- 
producing rays, which he says may sometimes be less than in 
normal vision. But he does not seem to notice the connexion 
between the red and the green sensitiveness, in contrary directions, 
shown in the intensity curves, and in my observations. (See T in 
these data.) 
S. 
Later Yieios of Professor Holmgren on Variations of 
Dichromic Vision, 1881 and 1884. 
Although Professor Holmgren was a supporter of Young’s colour 
theory, he did not agree in its original application to the explana- 
tion of colour-blindness. And when I was in communication with 
him in 1881 I learnt that, in consequence, although he used the 
terms red-blindness and green-blindness, he did not consider they 
really applied to the subjective sensations of dichromic patients, 
inasmuch as he believed that the two kinds always went together. 
But he continued to use the terms as a matter of convenience, in 
order to give an idea of the different objective behaviour, in sorting 
