THE PHENOMENON OF CONDUCTION. 



89 



the current that it is necessary to use to get a response. With the 

 battery or galvanic current, in fact, one may distinguish four stimuli, 

 the closing and the opening shock when the stimulating electrode 

 is the cathode and the closing and the opening shock when it is 

 the anode. The contractions resulting from these four stimuli are 

 designated usually as follows: The cathodal closing contraction, 

 CCC; the cathodal opening contraction, COC; the anodal clos- 

 ing contraction, ACC; and the anodal opening contraction, 

 A O C. Their relative efficiency as stimuli is given by the sequence 

 CCOACOAOOCOC, although this sequence is subject, 

 so far as the first two members are concerned, to some individual 

 variation. Certain pathological or traumatic lesions that cause the 

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



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. 



methods of stimulation. The nerve trunk under such circum- 

 stances fails to respond to either form of stimulus, induced or gal- 

 vanic. The muscle, on the other hand, while it fails to respond to 

 induction shocks, is stimulated by the galvanic current and shows 

 certain qualitative changes in its reactions to this latter form of 

 stimulation. For instance, under these conditions the A C C is ob- 

 tained with less current than the C C C, a relation which is just the 

 reverse of the normal. 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 degen- 

 eration. 



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 



