THE PHENOMENON OF CONDUCTION. 89 



by the use of these methods of stimulation. The nerve trunk 

 under such circumstances fails to respond to either form of stimulus, 

 induced or galvanic. The muscle, on the other hand, while it 

 fails to respond to induction shocks, is stimulated by the galvanic 

 current and, indeed, may show an increased irritability toward this 

 form of stimulus. Certain qualitative changes in the reaction of the 

 muscle to the galvanic current may also be noticed, for instance, 

 the A C C is sometimes obtained with less current than the C C 0, 

 and the contraction is more sluggish in character. This qualitative 

 and quantitative change in reaction to the galvanic current, and 

 the loss of irritability to the induced current, constitute what is 

 known as the reaction of degeneration. 



n 



Fig. 35. Two schemata to show the relation between the physical and the physio- 

 logical electrodes or poles. Each schema represents the forearm with the median nerve, 

 M. In / the stimulating electrode is the cathode ; the threads of current which have started 

 from the anode (the indifferent electrode) placed elsewhere, converge to this pole. Where 

 these threads enter the nerve we have a series of physiological anodes, a; where they leave, 

 a series of physiological cathodes, c. In // the stimulating electrode is the anode. The 

 threads of current leave this pole to traverse the body toward the indifferent electrode 

 (cathode). Where they enter and leave the nerve we have, as in the first case, physio- 

 logical anodes and cathodes, now, however, on the opposite sides of the nerve. 



Distinction between Physical and Physiological Poles. The 



facts stated above seem to show, at first sight, that by the 

 unipolar method we may obtain both an opening and a closing 

 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 



