62 GENERAL PROPERTIES OF LIVING TISSUES 



resistance of the secondary coil will practically 

 be nothing in comparison with the enormous 

 resistance of animal tissue. 



Eepeat the preceding experiment, introducing 

 in the secondary circuit a high external resist- 

 ance, i. e. a nerve. 



The secondary coil with many turns of fine wire 

 now causes a much greater deflection of the gal- 

 vanometer needle than the coil with fewer turns. 



Interrupter. Instead of making and break- 

 ing the primary circuit by hand, an automatic 

 interrupter is provided. The primary circuit 

 passes through a screw, the point of which con- 

 veys the current through a flat spring upon 

 which is mounted an iron disk opposite and near 

 to the core of wire in the primary coil. When 

 the current enters the primary coil, the core is 

 magnetized and draws upon the iron disk. The 

 spring, to which the disk is attached, is thereby 

 drawn away from the screw-point through which 

 the current is passing. Thus the current is 

 broken, and ceases to flow through the primary 

 coil ; the core no longer is magnetized, and re- 

 leases the iron disk ; the spring again makes 

 contact with the screw-point, the current is re- 

 established, only to be at once again broken. 

 Thus a rapid series of make and break induc- 

 tion currents is secured. 



