PHYSIOLOGIC APPARATUS 



747 



ment whereby the opposite ends of the semicircular wires can be made to dip 

 Sto cups 3 and 4, and into cups 5 and 6 alternately. . Two wires crowed m 

 the middle of the block serve to connect opposite pairs of cups. Wher 

 use, the cups are filled with clean mercury. The method of using the 



Current R^erser.-Tht positive and negative poles of thfe electric 

 cell are connected by wires with binding posts i and 2 respectively. 

 A key is interposed in the circuit. Wires are then earned from binding 

 posts 3 and 4 to the electrodes in connection with the muscle or nerve. 

 The rocker of the commutator is so turned that the ends of the sem cir 

 cular wires dip into cups 3 and 4. The direction of the current will be 

 onlhe closureof the circuit from r to 3, then from 3 along a wire to and 

 throughthetissueandbackto 4 ,andthencetothecell. the P 1 J 

 the rocker be now reversed so that the opposite ends of the semicircular 



FIG. 342. POHL'S 



A. Arranged as 

 rent deflector. 



reverse,; B, as a c, 





-' sssssrss? * - 



