CHAPTER III 



Simple Experiments Illustrating the Use of Electrical 

 Apparatus in Physiology 



1. CONNECT up a cell with a pair of wires, introducing a simple key 

 into the -circuit (Fig. 10). Place the free ends of the wires on the 

 tongue, and close and open the key. 



2. Repeat this experiment, but usen short-circuiting key (Fig. 14). 

 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 commutator, as shown 

 in Figs. 15, 17, and 18. Determine with pole-testing 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 l , t' 2 of the primary 

 coil of the inductorium, introducing 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. 22). 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. 



This is partly due to the fact that as the current of the primary 

 circuit is made and broken, induced currents (extra currents) are 

 formed in its own coils ; the make extra current of closure, being in 

 the opposite direction to the battery current, diminishes the make 

 induced current in the secondary circuit, while the break extra current 

 is cut off by the opening of the primary circuit, and therefore has no 

 effect on the induced current. The sharpness of the break effect is 

 also partly due to the fact that with the keys generally used the 

 opening of the primary circuit is more sudden than its closure. 



5. To show the existence of the "extra" currents, remove the 

 secondary coil altogether and connect up the primary coil with a 

 galvanic cell and keys in the way shown in Fig. 25. Place the 



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