Professor Dewar and I worked nearly twenty years ago. The eye of a frog has been carefully dissected out (the animal of course being dead, although the tissues of its eye still live), and it has been placed on the clay pads so that one pad touches the back of the eye while the other is in contact with the front of the eye—the cornea. We now place the eye in darkness by covering the troughs over with a bandbox, in which, however, we have left a small window which we can open and shut at pleasure, and the position of the window is such that if we place a light before it, the light will shine on the cornea of the little eye. Now I shut the key so as to allow any current that there may be to flow to the galvanometer. You see at once there is a very considerable current. That is the resting current of the eye in the dark. Mr. Brodie will now allow light to fall on the eye. You see at once the spot of light on the scale moves and indicates an increase in the first current. As light continues to act the current begins to diminish; but I now ask Mr. Brodie to take away the light and leave the eye in darkness. You see the moment the light was removed that the current again
