II.] 



EYEBALL CURRENTS 



23 



flashing lights, or a succession of colours, in accordance with 

 the accidents and irregularities of such coarse artificial disturb- 

 ance. And no doubt could we only detect it the physico- 

 chemical disturbance is attended by an electrical disturbance 

 The latter will, however, be most easily demonstrated to you 

 with an excised eyeball. 



12. Demonstration. Such an eyeball has been removed 



Light. 



FlG. 8. Frog's eyeball between unpolarisable electrodes for demonstration oi 

 the electrical effects of light and of electrical excitation. The circuit from the eye is 

 completed through a compensator, secondary coil, and a galvanometer. The arrows 

 through the eyeball and the galvanometer indicate the direction of the initial current 

 and of the normal response. Arrows near the compensator wires indicate the direction 

 of a compensating counter-current. 



as carefully as possible a few moments ago from a pithed frog. 

 " Carefully " in this connection means with as little compression 

 of the eyeball as possible, and in point of fact such compression 



