CHAP, ii.] THE CONTRACTILE TISSUES. 



67 



faradaic 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 instrument 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. 6. 



FIG. 6. THE MAGNETIC INTERRUPTOR. 



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

 brass pillars a and d by means of screws. Directly contact is thus 

 made the current, indicated in the figure by the thick interrupted line, 

 passes in the direction of the arrows, up the pillar a, along the steel 

 spring b, as far as the screw c, the point of which, armed with platinum, 

 is in contact with a small platinum plate on 6. The current 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 shewn in the figure). 

 From the primary coil p the current passes, by a connecting wire, 

 through the double spiral, m, and, did nothing happen, would continue 

 to pass from m by a connecting wire to the pillar d, 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 6, 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 f is so arranged that 

 when Q is drawn down a platinum plate on the under surface of b is 

 brought into contact with the platinum-armed point of the screw f. 



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