THE REACTION OF NORMAL AND ABNORMAL NERVE 151 



This procedure is commonly called the unipolar method of stimula- 

 tion (Chaveau). To begin with, the indifferent electrode is firmly 

 applied to some part of the body, while the stimulating electrode is 

 brought in contact with the region overlying the nerve or muscle to 

 be tested. The accompanying Fig. 89 may serve to illustrate the ar- 

 rangement generally employed in stimulating the muscles of the arm. 

 But practically every voluntary muscle in our body may be tested 

 in the same way, although its excitation is usually effected through 

 its motor nerve by applying the active electrode to the region in which 

 its nerve becomes most superficial. The location of these different 

 motor points may be determined with the help of Figs. 90 and 91. 



FIG. 89. SCHEMA TO SHOW THE UNIPOLAR METHOD OF STIMULATION IN MAN. 



The anode, +, is represented as the stimulating pole, applied over the median nerve. 

 The cathode, , is the indifferent pole. (Howell.) 



If the stimulating electrode is made anodic, it will be found that 

 neither the making nor the breaking of a weak galvanic current gives 

 rise to a contraction. If the active electrode is now made cathodic, a 

 contraction will be obtained on the making of this current. This re- 

 action is usually called the cathodic closing contraction (C.C.C.). On 

 repeating this procedure with a current of medium strength, it will be 

 noted that the anode also becomes effective, a contraction now resulting 

 both on the making and breaking of this type of current. These con- 

 tractions are designated respectively as the anodic closing (A.C.C.) 

 and anodic opening contraction (A.O.C.). The cathodic closure con- 



