1892-93.] Dr William Pole on Colour-Blindness. 
Ill 
WHITE 
YELLOW 
BLUE 
Diagram of the Colour Vision of the Middle Zone of the Normal Retina, 
as observed by Schelske. 
L. 
Investigations hy Professor Pick on the Dichromic Zone of the 
Retina^ 1874. 
The multiplicity of colour-sensations is confined to a small 
central part of the retina round the pole. Beyond this extends 
a zone which behaves like the retina of the red-blind eye ; and 
farther away, nearer the equator, is another zone, where all quali- 
tative sense of colour is lost. The following is the nature of the 
impressions given hy the same ray in the three zones respec- 
tively : — 
Polar Zone, 
Normal. 
Middle Zone, 
Dichromic. 
External Zone. 
Bed. Yellow or brown, according Grey or black, 
to luminosity. 
Yellow and green. Bright yellow. White. 
Blue. Paler blue. Grey. 
Violet. Blue. Grey. 
Blue-green. White or grey. Grey. 
