METHODS OF ELECTKICAL STIMULATION 55 



farther from the magnetic core. Once set, the inter- 

 rupter will begin to vibrate as soon as the primary 

 circuit is made. The outer binding posts are used for 

 the tetanizing current. The left-hand outer post and 

 the middle post are used when single induction cur- 

 rents are desired ; they connect directly with the ends 

 of the primary wire, thus excluding the interrupter. 

 These several connections upon the head-piece are 

 simply arranged and are all in view ; there are no con- 

 cealed wires. 



From the head-piece extend two parallel rods 

 cm. in length, between which slides the secondary coil, 

 containing 5000 turns of silk-covered wire 0.2 mm, in 

 diameter. Over each layer of wire upon the secondary 

 spool is placed a sheet of insulating paper. Each end 

 of the secondary wire is fastened to a brass bar 

 screwed to the ends of the hard-rubber spool. 



The brass bars bear a trunnion which revolves in 

 a split brass block, the friction of which is regulated 

 by a screw. The trunnion block is cast in one piece 

 with a tube 3 cm. in length, which slides upon the 

 side rods. A set screw, not shown in Fig. 14, holds 

 the trunnion block tube and the secondary spool at 

 any desired point upon the side rods. This screw 

 also serves to make the electrical contact between the 

 trunnion block tube and the side rod more perfect. 

 The secondary spool revolves between the side rods 

 in a vertical plane. When the secondary coil has 

 revolved through 90, a pin upon the side bar of 

 the secondary coil strikes against the trunnion block 



