Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 24 THE SIGNS OF LIFE [lect. has been nearly quite avoided by cutting the frog's head in half, taking up the fragment with forceps, and trimming away the orbit from the eyeball with scissors. The eyeball is now resting upon the clay pad of an unpolarisable electrode, the pointed pad of the second electrode touches the cornea, the actual contact being by a droplet of salt solution. The electrodes are con- nected to a galvanometer. The eyeball and electrodes are enclosed in a black box with a hole,
Eight lectures on the signs of life from their electrical aspect eightlectureson00wall Year: 1903 24 THE SIGNS OF LIFE [lect. has been nearly quite avoided by cutting the frog's head in half, taking up the fragment with forceps, and trimming away the orbit from the eyeball with scissors. The eyeball is now resting upon the clay pad of an unpolarisable electrode, the pointed pad of the second electrode touches the cornea, the actual contact being by a droplet of salt solution. The electrodes are con- nected to a galvanometer. The eyeball and electrodes are enclosed in a black box with a hole, tube, and shutter opposite the eye, so that when desired the latter can be exposed for any required time to light of any required strength. The connections are such that the fundus of the eyeball is attached to the south terminal, and the cornea to the north terminal, of the galvanometer as in Fig. 3 or in Fig. 8, with the keyboard unplugged. (The circuit includes a compensator and a secondary coil, to be used in our next Lecture.) O-OIO f 1 1 1 1 1 1 § 13. The initial cur- rent. — Notice as a first point that the natural cur- rent of the eyeball has given current through the galvanometer from N to S terminal, , that within the eyeball it has been from fundus to cornea. Notice further the fact that this current is rapidly de- clining. The spot deflec- , , ,. . r r , ted to your right is sink- —Normal declimng current of a frogs . '^ The rate and shape of decline resemble mg tO yOUr left towards those of a blaze current. j^S 2erO point* If WC could afford to wait, we should see the spot reach the zero and continue its journey to the opposite end of the scale, indicating to us that the eyeball current, at first directed from fundus to * The lecture-room is east and west, the former being the lecturer's end. The galvanometer is on a bracket fixed to the east wall of the room, and the movements of its suspended magnet are shown by a vertical spot of light reflected to a t
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