THP: PHENOMENA OF MUSCLE AND NERVE. 



63 



passes through its electrodes. We shall frequently speak of this as the interrupted 

 induction current, or more briefly the interrupted current ; it is sometimes spoken 

 of as thefaradic current, and the application of it to any tissue is spoken of as 

 faradization. 



Such a repeated breaking and making of the primary current may be effected 

 in many various ways. In the instruments commonly used for the purpose, the 

 primary current is made and broken by means of a vibrating steel slip working 

 against a magnet : hence the instrument is called a magnetic interrupter. See 

 Fig. 15. 



The two wires x and y from the battery are connected with the two brass pillars 

 a and d bv means of screws. Directly contact is thus made current, indicated 



FIG 





The Magnetic Interrupter. 



in the figure by the thick interrupted line, passes in the direction of the arrows, 

 up the pillar a, along the steel spring ft, as far as the screw c, the point of which, 

 armed with platinum, is in contact with a small platinum plate on b. The cur- 

 rent passes from b through c and a connecting wire into the primary coil p. Upon 

 its entering into the primary coil, an induced (making) current is for the instant 

 developed in the secondary coil (not shown in the figure). From the primary coil 

 p the current passes, by a connecting wire, through the double spiral w, and. did 

 nothing happen, would continue to pass from m by a connecting wire to the pillar 

 c?, and so by the wire y to the battery. The whole of this course is indicated by 

 the thick interrupted line with its arrows. 



As the current, however, passes through the spirals m, the iron cores of these 

 are made magnetic. They, in consequence, draw down the iron bar e, fixed at the 

 end of the spring ft, the flexibility of the spring allowing this. But when e is 

 drawn down, the platinum plate on the upper surface of b is also drawn away from 

 the screw c, and thus the current is " broken " at b. (Sometimes the. screw / is 

 so arranged that when e is drawn down a platinum plate on the wider surface of b 

 is brought into contact with the platinum-armed point of the screw / The cur- 

 rent then passes from b. not to c, but to /, and so down the pillar d, in the direction 

 indicated by the thin interrupted line, and out of the battery by the wire y, and is 

 thus cut off from the primary coil. But this arrangement is unnecessary.) At the 

 instant that the current is thus broken and so cut off from the primary coil, an 

 induced (breaking) current is for the moment developed in the secondary coil. But 

 the current is cut off not only from the primary coil, but also from the spirals m ; 

 in consequence, their cores cease to be magnetized, the bar e ceases to be attracted 

 by them, and the spring ft, by virtue of its elasticity, resumes its former position 



