ELECTRO-PHYSIOLOGY. 



583 



current set up in a second wire placed near it. The strength of the 

 induced current may be increased by placing a bundle of soft iron 

 wires in the interior of the primary coil. By using a large number 

 of turns of wire in each coil the effect is greatly increased, because 

 each turn of the primary coil induces a current in each of the turns 



Fig. 218. DuBois-Reymond's Induction Apparatus. (WALLER.) 



rith 



The numbers 1 to 7 indicate the terminals and contact screws connected 

 the primary coil. 



For single shocks the two battery wires are to be connected with the termi- 

 nals 4 and 5, which are at the two ends of the primary wire. 



(a) Unmodified shocks are obtained when a key is used to interrupt one of 

 the wires. 



(1>) Reduced shocks are obtained when a key is used short-circuiting the 

 primary wire. 



(c) For repeated sJiocks (ordinary) the two battery wires are to be inserted 

 at 1 and 6. The circuit now includes the spring interrupter and the wire of 

 the electro-magnet by which the circuit is made and broken at the contact 

 screw 3; the contact screw 7 is kept out of use by being lowered. 



(d) For repeated shocks (modified) the battery wires are left, as before, at 

 1 and 6. A short, thick side wire is placed between 2 and 4. The contact 

 screw 3 is raised out of range of the spring, and the contact screw 7 is raised 

 until it comes within range of the spring. 



The electrode wires arc in each case connected with two terminals (not seen 

 in figure) forming the two ends of the secondary wire. 



the second, and all these small effects summed up produce 

 single greatly increased effect. The opening shock is stronger 

 than the closing shock, so that if repeated induction shocks are sent 



I rough a tissue- for some time polarization effects are set up. To 



