112 Proceedings of Royal Society of Edinhurgli. [sess. 
In a later publication (1879) he connected these appearances 
more explicitly with congenital colour-blindness. He said : — “ In 
a considerable fraction of all mankind (more than one-twentieth) 
the polar zone of the retina is also wanting in the normal capability 
of distinguishing the varieties of colour. Such individuals are called 
‘colour-blind.’” It is probable that this state simply consists in 
the fact that the property of the retina, which in the normal eye 
exists in the middle zone, is here present also in fovea centralis. 
Total colour-blindness will further ensue if the whole retina takes 
the properties of the extreme outer zone of the normal eye. 
M. 
Remarhs hy Von Kries on the Dichromic Zone of the Retina, 1882. 
This author discusses the whole subject very fully ; and on the 
main points he agrees with other investigators. He fully substan- 
tiates the existence of an intermediate annular dichromic zone, 
where only yellow and blue are visible, the red, orange, and yellow- 
green being transformed into the former, and the blue-green and 
violet into the latter. 
The limits of the zones are somewhat irregular and variable ; 
the vision of green in the smallest extending some 30° or 40° 
from the centre ; that of red is a little more ; then comes the blue 
and yellow ring extending to about 65°, and the peripheral or 
colourless space filling up the remainder. The divisions are not 
sharp, but the changes run gradually into each other. 
The author also discusses the theory, and points out the diffi- 
culties with the Young-Helmholtz hypothesis. 
N. 
Hess’s Observations on the Variable Colour Vision of the Normal 
Retina. 
It had been remarked in previous investigations that the transi- 
tions between the different colour zones of the normal retina were 
not sudden, but gradual, and this author determined to watch more 
carefully than formerly the whole of the colour changes, and the 
effect of various exciting rays, in every position of their passage 
from the centre to the circumference. The trials were made first 
