APPARATUS , 11 



current the fall occurs so soon after the rise that the 

 tissue is not capable of -responding to it in the con- 

 ditions of the experiment. 



b. Rapidly repeated induction currents (tetanis- 

 ing currents). In order to obtain a rapid series of in- 

 duction currents the inductorium is supplied with a vi- 

 brator (v) and a small coil (m) with soft iron core (Fig. 3). 

 One binding screw of the primary coil is connected with 

 the coil of wire of m, and the other end of this to a bind- 

 ing screw (p 2 ) at the base of the machine (Fig. 3). 

 Change the battery wires from the screws at the top of 

 the machine to those at the base. Screw down c so that 

 it just touches v. The screw c can be fixed by the set- 

 screw s.s. Leave the connections of the secondary coil 

 and electrodes as before. Close the primary circuit (if 

 necessary flick the hammer h), the hammer will be set 

 in rapid oscillations, each downward movement of the 

 hammer breaking the primary circuit, each upward 

 movement making it. Put the index of the secondary 

 coil at 35 cm., place the electrodes on the tongue, and 

 gradually push the secondary towards the primary coil ; 

 note the position at which the shocks are first felt. Note 

 also the position at which the shocks cannot be borne 

 comfortably. The method in which the primary current 

 is made and broken will be easily understood from the 

 figure. When the current is passing in the primary coil, 

 v is in contact with c, but since the current also passes 

 round the coil m the soft iron core of this coil becomes 

 magnetised, and consequently attracts the plate hi as 

 this goes down the contact of v and c is broken,, hence 

 the current ceases to pass in the primary coil, the core 

 of m is no longer magnetised, the plate h flies up, v 



