STIMULATION OF MUSCLE AND NERVE 119 



The law revealed by this experiment may be 

 thus expressed. The same stimulating current 

 has a greater stimulating effect when it coincides 

 in direction with a pre-existing current, and a 

 lessened effect when it is opposed in direction to 

 a pre-existing current. This law explains the 

 interference observed between stimulating cur- 

 rents and demarcation or injury currents of nerve 

 and muscle (see page 292). 



3. Place a drop of saturated solution of sodium 

 chloride on the nerve in the extrapolar region 

 near one of the non-polarizable electrodes. 

 Record the irregular tetanus (chemical stimu- 

 lation) on a slowly moving drum. Make the 

 polarizing current. 



Note that the tetanus is increased when the 

 cathode is nearer the stimulating solution, but 

 diminished when the anode is nearer. 



Hence the irritability of the nerve is k altered 

 during the passage of the electric current (elec- 

 trotonus); 1 it is increased in the neighborhood 

 of the cathode (catelectrotonus) and is diminished 

 in the neighborhood of the anode (anelectro- 



1 The change in the excitability of the nerve produced by 

 the electric current is so generally called electrotonus that the 

 term cannot well be, changed. It should not be confused with 

 the electrotonus described on page 000, though it is possible 

 that the two phenomena have a similar if not identical first 

 cause. 



