STIMULATION OF MUSCLE AND NERVE 161 



The law of polar excitation holds good then 

 for the induced as well as the galvanic current. 

 In fact, there is no essential difference between 

 the physiological effects of induced currents and 

 very brief galvanic currents. 



Increasing the intensity of the induced cur- 

 rent increases at first the excitation (height of 

 contraction). At length, however, with ascend- 

 ing currents, a point is reached beyond which 

 further increase in strength is followed first by 

 the diminution and at length by the disappear 

 ance of contraction. With still higher intensi- 

 ties, the contractions reappear. This gap in the 

 contraction series is explained by the increasing 

 depression of irritability at the anode blocking 

 the cathodal impulse ; when the intensity is still 

 further increased, the opening of the current acts 

 as a stimulus. A similar result may be secured 

 with the galvanic current. 



APPARATUS 



Normal saline. Bowl. Pipette. Towel. Simple key. 

 Non-polarizable electrodes. Nerve holder. Potter's clay 

 mixed with 0.6 per cent solution of sodium chloride. 

 Saturated solution of zinc sulphate. Muscle clamp. 

 Stand. 13 wires. Kymograph, (Jfyzed paper. Two 

 muscle levers. Thread. Rheochord. Two dry cells. 

 Moist chamber. Glass plate. Ice. Paraffin paper. Cork 

 clamp. Pole-changer. Beaker. Tripod. Sodium chloride, 

 11 



