EXCITATION OF NERVE~AND MUSCLE BY GALVANIC CURRENT 5 5 



mercury key is introduced into the circuit (Fig. 48). Beginning with 

 a very weak current, the rider of the rheochord being brought near to 



the end a of the rheochord wire (see Figs. 19, 20), determine the effect 

 upon the nerve, as indicated by the contraction of the muscle, of 



