CHAPTER III 



SIMPLE EXPERIMENTS ILLUSTRATING THE USE OP 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 use a 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 1 , 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 



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