STIMULATION OF MUSCLE AND NERVE 147 



Polar Fatigue. Connect non-polarizable elec- 

 trodes through a simple key with a dry cell. 

 Fatigue a sartorious muscle by opening and clos- 

 ing the galvanic circuit (leave a brief interval 

 between opening and closure). Closure will at 

 length be followed by no contraction. Arrange 

 an inductorium for single induction currents (the 

 pole-changer may be placed in the primary cir- 

 cuit as a simple key). Test now the irritability 

 of the muscle by stimulating it with single induc- 

 tion currents. 



The muscle will be irritable except in the cath- 

 odal region. The fatigue has been local (polar). 



Opening and Closing Tetanus. 1. Arrange a 

 moist chamber with a muscle lever to write on a 

 smoked drum. Place two non-polarizable elec- 

 trodes in the moist chamber and connect them 

 through a pole- changer with a dry cell. Make a 

 nerve muscle preparation from a frog that has 

 just been brought from a cold room into the warm 

 laboratory. Secure the femur in the femur clamp 

 of the moist chamber. Let the nerve rest on the 

 non-polarizable electrodes. Attach the muscle 

 to the lever. Bring the writing point against the 

 slowly moving drum. Close the key. 



If the frog has been well cooled (below 10 C.), 

 the muscle will fall into tetanus both on closing 

 and on opening the circuit. Note that the curve 



