STIMULATION OF MUSCLE AND NERVE 125 



After three minutes' rest, bring the cathode next 

 the muscle and make the polarizing current as 

 before. Then stimulate again with a make in- 

 duction current of the same intensity as before. 



Contraction will be absent, or at most very 

 weak. The impulse will be blocked in the 

 cathodal region. In truth, during the passage of 

 strong or protracted currents, the conductivity is 

 more diminished in the cathodal than in the 

 anodal region. 



Grlitzner and Tigerstedt believe that the open- 

 ing contraction is due to the stimulation of the 

 nerve or muscle by the polarization current 

 which appears when the galvanic current is 

 broken. The polarization current may be said 

 to be closed when the galvanic current is opened. 

 These observers, therefore, hold that stimulation 

 takes place only at closure. 



We are now in a position to account for the 

 phenomena described by the law of contraction. 

 The irritability of the nerve is increased at the 

 cathode on closing, and at the anode on opening 

 the galvanic current. This rise of irritability 

 stimulates the nerve. The rise at the cathode is 

 a more effective stimulus than the rise at the 

 anode ; consequently with weak currents the first 

 stimulus to produce contraction is cathodal, i. e. 

 at the closure of the circuit. As the current in- 



