1 6 PRACTICAL PHYSIOLOGY 



and so on automatically. It will be observed that 

 the primary circuit is never actually broken, but 

 only short-circuited. 



The above-described apparatus having been 

 studied, the following experiments are to be per- 

 formed : 



1. Connect up a cell with a pair of wires, intro- 

 ducing a simple key into the circuit (Fig. 9). Place 

 the free ends of the wires on the tongue, and close 

 and open the key. 



2. Repeat this experiment, but use a short-cir- 

 cuiting key (Fig. 12). Note that the effect of the 

 current upon the tongue is now only felt when the 

 key is open. 



3. Connect a cell with electrodes through a com- 

 mutator, as shown in Fig. 13. Determine with 

 pole-reaction paper which is the anode and which 

 the kathode in the two positions of the bridge of 

 the commutator. Verify this by following out the 

 course of the wires. 



4. Connect a cell with the upper terminals, T*, 

 T 2 , of the primary coil of the inductorium, intro- 

 ducing a simple key into the circuit. Connect a 

 pair of electrodes through a short-circuiting key with 

 the terminals of the secondary coil, and slide this 

 coil to some distance from the primary (Fig. 17). 

 Place the electrodes on the tongue. Alternately 

 close and open the key in the primary circuit. 

 Notice that induction shocks are obtained on 

 making and breaking the primary circuit, but not 

 during the passage of the current. Notice that the 

 break shocks are much sharper than the make. 



