180 P t oceedings of the Poycd Society 
tance of one foot, a variation to the extent of about 100 degrees 
was observed. At a distance of 10 feet, with ,-J-g-th part of the 
amount of light, the effect was not 1 degree, but 20 degrees, or £th 
of the total amount observed at 1 foot. 
3. The action of light on the electro-motive force of the liv- 
ing eye in cats and birds (pigeon and owl) has been observed. 
In our earlier experiments we found great difficulty in observing 
sensitiveness to light in the eyes of mammals and birds when these 
were removed with the utmost despatch from the orbit of the animal 
immediately after death. This was evidently owing to the fact 
that the sensibility of the nervous system in these animals disap- 
pears quickly after the withdrawal of healthy blood. It therefore 
became necessary to perform the experiment on the living animal. 
This was done by first putting the cat or bird under the influence 
of chloroform, then fixing it by a proper apparatus, so that the 
head was perfectly immovable, and lastly removing the outer wall 
of the orbit with as little disturbance to the ciliary vessels as 
possible. The optic nerve was now cut, the transverse section 
directed upwards, and the clay points of the electrodes were now 
adjusted, one to the transverse section of the nerve, and the other 
to the cornea. With these arrangements we at once found a strong 
current extremely sensitive to light. 
4. The effect was traced into the optic lobes of a living pigeon 
under chloroform. The following were the results of this observation: 
(a.) when one pole was applied to the left optic lobe, and the other 
to the cornea of the right eye, a deflection was obtained, which was 
sensitive to light; (b.) when the pole was removed from the right eye, 
and applied to the cornea of the left, a smaller deflection was ob- 
tained, also sensitive to light; and (c.) when light was allowed to 
impinge on both eyes, while the one pole was in contact with either 
eye, and the other with the left optic lobe, the result was nearly 
double that produced by the impact of light on one eye alone, either 
right or left. These effects may be explained by the decussation 
of the optic nerves in the optic commissure. 
5. The eye of a snake * was examined, and in its action resembled 
that of the frog. 
* Kindly sent us by Mr Bartlett of the Zoological Gardens, Kegent’s Park. 
We have also to acknowledge the kindness of Mr Lloyd, manager of the Crys- 
