42 



THE SIGNS OF LIFE 



[LECT. 



help you to understand the lecture, and that the hearing of the 

 lecture may help you to understand the paper. 



23. The effects of tetanisation. Experiment I. When one 

 has seen that the stimulation of an eyeball by light arouses 



, Light. 



InducCorium. 



FlG. 19. Frog's eyeball between unpolarisable electrodes for demonstration of 

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

 completed through a compensator, secondary coil, and 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 compensating counter-current. 



a positive electrical response (and that any mechanical dis- 

 turbance arouses current in the same direction), he naturally 

 thinks of electrical excitation, and expects to find that 

 if the retina is stirred up to activity by such means, it will 

 manifest current in that same positive direction. The ex- 



