THE PHENOMENON OF CONDUCTION. 93 



it will be found that the four stimuli are of different efficiencies. 

 The usual relationship is expressed by the sequence C C C > 

 A C C > A O C >C O C, although this sequence is subject to some 

 individual variation. Pathological or traumatic lesions that 

 cause the degeneration of the nerves may be revealed by the use 

 of these methods of stimulation. The nerve trunk under such 

 circumstances fails to respond to either form of stimulus, in- 

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

 fail to respond to induction shocks, is stimulated by the gal- 

 vanic current, and, indeed, may show an increased irritability 

 toward this form of stimulus, although the contractions are 

 more sluggish in character than in a muscle with a normal nerve 

 supply. 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 C. 

 This qualitative and quantitative change in reaction to the 

 galvanic current, and the loss of irritability to the induced cur- 

 rent, constitute what is known as the reaction of degeneration. 



-M-t 



n 



Fig. 36. 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, 

 Mt 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 x explained when we remember that in the 



