110 Proceedings of Boyal Society of Edinburgh. [sess. 
obviously from them that spectral red, green, and blue or violet are 
not the variable elements of the colour sense ; but rather, on the 
one hand, the pure yellow and blue, and, on the other hand, the 
pure red and green ; ^.e., those two pairs of colours which I have 
designated as the fundamental or the original pairs of colours. 
J. 
Hess’s Case of Dichromatism in One- Half of an Eye., 1890. 
Two months previously the vision of the patient was perfectly 
normal, but at the time of his examination the nasal half of his 
left eye had become colour-blind, while the temporal half remained 
normal. Tests were applied, both with pigments and spectral 
colours, and it was found that the affected half presented all the 
symptoms of nearly complete dichromic vision. The sensitiveness 
to red and green was almost entirely lost, but that to the yellow 
and blue remained, although weaker. The white was slightly 
lessened in luminosity, but not changed in colour. 
K. 
Schelske’s Experiments on the Dichromic Zone of the Retina, 1863. 
This writer tested the vision of the middle zone of the retina 
with Maxwell’s revolving discs, and obtained the following 
equations : — 
45 yellow -1- 55 blue =18 white + 82 black. 
24 yellow 4-76 black = red. 
41 yellow 4- 59 blue = dark green. 
52 yellow 4-48 blue = light green. 
10 yellow 4- 43 black 4- 47 white = light green. 
The author fully admits the analogy of the case with congenital 
dichromic vision. To illustrate this, however, I have plotted the 
above equations in a diagram, which may be compared with my 
own and others of the same kind, as given in the Philosophical 
Magazine for July 1892. The author only gives the general names, 
and not the exact nuances of the test colours used ; but the general 
correspondence will be quite evident. 
