94 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



nerves of the brachial plexus and other nerve trunks may be 

 stimulated very readily through the skin. When the induction 

 current is used no distinction is made between the cathodic and 

 anodic effects. When, however, the battery current is employed 



M. triceps (caput 



tt. lambricales 



Fig. 36. — Motor points in upper extremity. 



one may make the stimulating electrode either anode or cathode, 

 and under these circumstances a marked difference is observed 

 in the strength of 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 open- 

 ing shock when the stimulating electrode is cathode and the 

 closing and the opening shock when it is anode. The con- 

 tractions resulting from these four stimuli are designated usually 

 as follows: The cathodol closing contraction, C C C; the cathodal 

 opening contraction, C C; the anodal closing contraction, 

 A C C; and the anodal opening contraction, A C. If the minimal 

 amount of current necessary to give each of these contractions 

 is measured in milliamperes by means of a suitable ammeter, 



