820 7 General Notes. [August, 
layer of the retina; both the latter phenomena were discovered 
by Boll. But Professor Engelmann, of Utrecht, adds another to 
the objective disturbances caused by light in the retina, namely, 
that of movement of the inner segment of the retinal cones. The 
inner segments of the cones become shorter under the influence 
of light and longer when the light is removed. The amount of 
this difference in length owing to illumination varies in different 
animals. The difference was most marked in the fish and frog. 
In a fish which was kept eight hours in the dark the inner cone 
segments, measuring from the mem. lim. ext. to the inner pole of 
the cone ellipsoid, had a length of about 50; after remaining 
several hours in diffuse daylight the length of the inner cone 
segments in the same animal was only about 5#. In preparing 
the retina for observation the eye-ball was rapidly excised and 
plunged in 3.5 per cent nitric acid, or for several minutes was 
warmed to 70°—80° C. in 0.5 per cent salt solution. 
A frog which has been kept in the dark shows maximal con- 
traction of the cones after several minutes exposure to diffuse 
daylight. All parts of the visible spectrum produce the change 
in question, but the more refrangible rays have apparently most 
marked influence. It is apparently the inner cone segment itself 
which is directly affected by the stimulus. The movement of the 
cones and of the epithelial pigment seems to be under the con- 
trol of the nervous system; for if an animal which has been 
kept long enough in the dark to bring about maximal lengthen- 
ing of the cones and retreat of the pigment, be exposed to light 
so that only one eye is illuminated, the influence of the light is 
manifested by both retinas; but if the brain has been previously 
destroyed, the contraction of the cones and the moving inward of 
the pigment occur only in the eye which is directly exposed to 
light. We may, therefore, consider that the movements in ques- 
tion are reflex actions, and that the optic nerves contain motor 
fibers for the protoplasm of the cones and of the retinal epithel- 
ium. Engelmann declares also that light acting directly upon 
the skin of a frog whose head is kept in the dark, brings about 
the same retinal changes as does light falling directly upon the 
eyes.—Phliiger’s Archiv., Bd. 35, S. 498. 
PSYCHOLOGY. 
that another should do to himself. The converse of this propo- 
sition, as uttered by Christ, imposes a greater proportion of active 
‘measures, Both are relatively carried into practice to the degree 
a which the wishes of men are subordinated to their intelligence. 
