CHAPTER XXIX. 



EXPERIMENTS ON NERVE AND MUSCLE WHICH 

 CAN BE DONE WITHOUT RECORDING. 



Contraction of the muscle is taken as the index of the excitation 

 of the nerve. 



Galvani's experiment. Raise the nerve upon the metal 

 seeker and with the latter touch one of the pins which hold 

 the skin down a contraction of muscles will occur. Contraction 

 with metals. 



The pin and seeker form a galvanic couple, the current from 

 which stimulates the nerves at the moment of contact and of 

 separation. Repeat the experiment with "electric forceps." 



A simple form of the latter consists of a copper and a zinc 

 wire twisted round each other, the free ends of which are 

 separated at one extremity (Fig. 30). 



FIG. 31. Electric forceps. 



Difference of make and break induction shocks. Use 

 single induction shocks, slide the coil to 30 cm and find the 

 minimal opening shock which will excite the nerve, as shown 

 by the contraction of muscles. 



The first evidence of this will be twitching of the toes. 



Gradually move up the S coil until the induction current 

 at closure also produces an effect, and note the distance in 

 each case. 



Weaker currents are required than were necessary in the 

 trials upon your own tongue. The nerve is more excitable. 



