90 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



shock at either the cathode or anode, a result which is in 

 apparent contradiction to the general law that the making or 

 closing stimulus occurs only at the cathode and the breaking 

 or opening stimulus only at the anode. This apparent contra- 

 diction is readily explained when we remember that in the 

 unipolar method the active electrode rests upon the skin over the 

 nerve, and that the threads of current radiating from this point 

 enter the nerve at one point and leave it at another. Evidently, 

 therefore, so far as the nerve is concerned, there will be an anode 

 where the current is considered as entering the nerve and a cathode 

 where it leaves it, so that under the active electrode, whether this 

 is physically an anode or cathode, there will be, as regards the 

 nerve, a series of what may be called physiological cathodes and 

 anodes. The closing shock arises at these cathodes, the opening 

 shock at the anodes. The position of the series of anodes and 

 cathodes will vary according as the active electrode is an anode 

 or cathode, as is indicated in the accompanying diagram (Fig. 35). 



