68 GENERAL PROPERTIES OF LIVING TISSUES 



current is in the same direction as the primary 

 current before the break. 



The Extra Currents at the Opening and Closing 

 of the Primary Current. 1. Remove the secon- 

 dary coil from the inductorium. Connect posts 

 1 and 2 of the primary coil with a dry cell, inter- 

 posing a simple key. Fasten the ends of the 

 electrode wires in these same 

 posts. Close the primary cir- 

 cuit. Place the electrode 

 f C Y^ J } points against the tongue. 



I U / Open the key. 



A shock from the self- 

 induced current developed in 

 the primary coil will be felt. 

 Draw a diagram of the circuits. 

 2. Connect a dry cell through 

 a key to the metre posts of the rheochord (Fig. 

 18). Connect the positive post and the slider to 

 the primary coil of an inductorium arranged for 

 single induction currents. Bring wires from these 

 posts of the primary coil through a simple key 

 to the nerve of a nerve-muscle preparation. Close 

 the key in the primary circuit. Open and close 

 the key in the nerve circuit. The muscle will 

 contract at closure and possibly at opening. By 

 means of the slider, weaken the current through 

 the primary coil until opening and closing the 



