82 



PRACTICAL PHYSIOLOGY 



current may pass to the electrodes, and use them as the wires in 

 the last experiment. Note the effect on the tongue of the sudden 

 appearance and disappearance of the current induced in the 



FIG. 87. Arrangement for single induction shocks, using galvanic cell. 



secondary coil each time the primary circuit is made or broken 

 by means of the mercury key. 



The experimenter can thus apply induced shocks at will. 



The results of making and breaking the primary circuit may be 

 recorded on the following form : 



Making Primary. 



Breaking Primary. 



2. A Series of Induced Shocks. Add to the primary circuit fitted 

 up as above a vibrating spring and a mercury cup (Fig. 88). At 



FIG. 88. Series of Induced Shocks. 



1. Induction Coil. 

 4. Mercury Key. 



5. Friction Key. 



6. Vibrating Spring with Cup 



containing Mercury. 



each vibration the spring makes and breaks the circuit. The rate 

 of vibration can be varied by altering the length of the spring. 



