124 GENEKAL PROPERTIES OF LIVING TISSUES 



torium arranged for single induction currents. 

 Lead from the other stimulating electrode to a 

 piece of nerve or muscle about 4 cm. long, and 

 thence to the secondary coil. The introduction 

 of this great resistance will keep most of the 

 polarizing current in the short bridge of nerve 

 between the polarizing electrodes. Without this 

 resistance, the polarizing current would pass 



through the stimulating 

 circuit in preference to 

 crossing the nerve be- 

 tween the stimulating 

 electrodes. Observe that 

 the nerve impulse cre- 

 ated by the stimulus 

 must pass through the 

 Fig. 33. cathodal region, if the 



current be descending, or 



the anodal region, if the current be ascending, in 

 order to reach the muscle. 



Find the position of the secondary coil at 

 which the muscle will barely contract on making 

 the stimulating current. Arrange the pole- 

 changer to bring the anode between the stimu- 

 lating electrodes and the muscle, and make the 

 polarizing current. Stimulate with a make in- 

 duction current during the passage of the polar- 

 izing current. Open the polarizing current. 



