8 



ELEMENTARY PHYSIOLOGY. I. 



the experiment with these. A sharp prick will be felt 

 on closing the key, there will be more or less pricking 

 sensation during the whole period the current passes, 

 and a slight additional prick when the key is opened. 

 When a current is sent into a circuit the current is said 

 to be 'made/ and when it is cut off from a circuit it is 

 said to be 'broken.' Thus the making of a current is a 

 stronger stimulus than the breaking of the current. In this 

 experiment there is an easily appreciable effect during 

 the passage of the current; the extent of such effect 

 varies (as will be seen later) in different tissues. 



4. Induction coil. Faradic currents. The induc- 

 tion coil (Fig. 3) consists essentially of a coil of thick 

 insulated copper wire the primary coil P and a coil of 



Fig. 3. 



thin insulated copper wire of many turns the second- 

 ary coil S. The ends of the primary coil are connected 

 with the screws >/, p 2 '. The ends of the secondary coil 



