the American Journal of Science and Arts, You. XIII, Jan., 1877.] 
Observations on a properly of the Retina, first noticed by Tait; by 
Ogden N. Rood, Professor of Physics in Columbia College. 
In the Edinburgh Proceedings, 1869-70, vii, p. 605-607, 
Tait described an interesting observation, which has perhaps 
some bearing on Thomas Young’s theory of color. While suf- 
fering from indisposition, he noticed each time on awakening 
from a feverish sleep, that the flame of a lamp seen through a 
ground-glass shade, assumed a deep red color, the effect lasting 
about a second. He suggests that the nerve fibrils in the 
retina also partook of sleep, and on awakening the green and vio- 
let nerves resumed their function somewhat later than the red. 
I have in my own case noticed some instances, which seem to 
point out that after a nervous shock, sudden or prolonged, the 
green nerves (adopting the theory of Young,) recover their 
activity later than the red, and probably later than the violet 
nerves. The first observation was made twenty jmars ago while 
recovering from the effects of chloroform, which had been 
administered by a dentist, well known at that time in Munich. 
Upon regaining consciousness, and raising my eyes to the face 
of the operator, I was a little surprised at not having previously 
remarked his unusually ruddy complexion, but the next instant 
saw that this was due to an optical illusion, for his hair 
appeared of a bright purplish-red hue. The singular appear- 
ance lasted perhaps a couple of seconds, when his hair resumed 
its natural color, which was white. This observation corresponds 
with that made by Tait. 
I give now an instance, where chronic effects of a similar 
character were noticed by me for a couple of weeks continuously, 
during convalescence from typhoid fever. In this case white 
objects appeared of a not very intense orange-yellow hue, the 
general effect on a landscape being such as is produced by the 
orange-yellow rays of the setting sun. Here the activity of the 
green and violet nerves was diminished relatively to that of the 
red. The auditory nerve was also evidently affected during 
the same period, but precisely in what way I did not ascertain. 
It is a matter of yearly observation with me, that effects, 
similar in kind with those first noticed, are produced by pro- 
longed exposure to bright white light out of doors. Under 
such circumstances white objects no longer appear pure white, 
but are tinted plainly purplish-red, and rather dull greens 
assume a gray hue, as though all the green in them had been 
neutralized, while strong greens are considerably reduced in 
intensity (saturation.) Upon leaving the blinding glare and 
entering a darkened room, it often for several seconds appears 
filled with a greenish haze. 
Two of these cases and, probably that of Tait, point out, that 
our apparatus for the reception of waves of light of medium 
length, is more liable to be over-strained bv nervous shocks or 
by prolonged excitation, than is the case with those designed 
for the reception of waves of greater or lesser length. Nervous 
derangement and prolonged excitation, are then 
may produce temporary green color-blindness.