112 
Proceedings of the Royal Society 
We have carried out, since last communication, several distinct 
sets of observations : — 
1. We have proved that though there is no difficulty in obtain- 
ing a strong current from the skin of the frog, this current is not 
affected by light. This observation demonstrates that the pigment 
cells of the skin in the vicinity of the cornea have nothing to do 
with the results obtained. 
2. The current obtained from a mass of the pigment cells of the 
choroid does not exhibit any sensitiveness to light. 
3. The subcutaneous injection into the frog of Woorara, 
Santonin, Belladonna, and Calabar bean, does not destroy the 
sensibility of the retina to light. 
4. As to the action of the anterior portion of the eye. On care- 
fully bisecting an eye of a frog, so as to remove completely the 
anterior portion, including cornea, aqueous humour, iris, ciliary 
muscle, and lens, and on bringing the retina into actual contact 
with one of the clay pads, we readily obtained a large deflection, 
which was as sensitive to light as when the whole eye was employed, 
thus eliminating any possibility of the contraction of the iris under 
the stimulus of light having to do with the results previously 
obtained. 
5. On using the anterior portion of the eye so that the cornea 
and posterior surface of the crystalline lens were the poles, we 
obtained a large deflection, which was, however, insensible to light. 
6. The sclerotic and nerve without the retina, in the same man- 
ner, gave a large natural electro-motive force, also not sensitive. 
7. The distribution of the electro-motive force between the dif- 
ferent portions of the eye and cross section of the nerve may be 
stated as follows : The most positive structure is the cornea, then 
the sclerotic, then the longitudinal surface of the nerve ; the cornea 
is also positive to the posterior surface of the crystalline lens, and 
the retina itself seems to be positive to the transverse section of the 
nerve. 
8. As to the effects 'produced by lights of different intensities . — If a 
candle is placed at a distance of one foot from the eye, and then is 
removed ten feet, the amount of light received by the eye is exactly 
one hundredth part of what it got at a distance of one foot; whereas 
the electro-motive force, instead of being altered in the same pro- 
