AFTER ELECTRICAL STIMULATION. 257 



coil of 7110 turns was mounted so as to revolve on a vertical axis. 

 The ends of the spiral terminate in slender plates running in circular 

 troughs filled with mercury, of which one is placed above, the other 

 below the revolving coil. These channels communicate with the 

 stimulating electrodes. The coil is made to revolve by means of a 

 pulley. If a strong magnet or the primary coil of an induction 

 apparatus through which a current is passing, be brought into the 

 neighbourhood of the revolving coil, and if the rate of revolution is 

 high enough, currents in alternately opposite directions are obtained, 

 which are sufficiently strong and physiologically equal. The strength 

 of the currents may be varied on the one hand by changing the 

 number of elements which supply the primary current, on the other 

 they may be adjusted with the utmost delicacy by altering the posi- 

 tion of the primary coil or magnet. With only i Daniell and 20 

 revolutions per second, I got tetanus with sensitive preparations 

 when the axes of the two coils (when parallel) w r ere 9 cm. distant 

 from each other, the most superficial layers of the two coils being 

 25 mm. apart. In the experiments I am about to describe, 3 Daniells 

 gave the primary current, the coils were as near together as possible, 

 and the number of revolutions' amounted to about 20 per second, 

 corresponding to twice as many induction currents. 



An induction apparatus was also used in which the primary coil was 

 replaced by a single conducting ring. A flat wooden ring (vulcanite 

 would have been a better material) was made 87 mm. in diameter 

 and 30 mm. in width. Around this 1 1 20 turns of thin copper wire 

 were wound. Then a second ring w r as made of the same width but 

 somewhat larger. This encircled the first ring, and a space was left 

 between the two for a thin copper ring 104 mm. in diameter. The 

 copper ring was nearly the same width as the wooden rings (25mm.). 

 A slit was made in it so that it did not form a closed circuit. It 

 consisted of a circularly bent strip of copper, the ends of which 

 were brought into electrical continuity by means of terminals which 

 communicated with wires from the battery. The primary circuit thus 

 constituted required a special interrupter. For this purpose, I used 

 either a wheel provided with twelve copper points which passed in 

 quick succession through a vessel of mercury, or one of Wagner's 

 hammers adapted for the purpose. This was set in action by a 

 special cell, and besides interrupting its own current, effected 

 the regular interruption of the above-mentioned primary circuit. 

 The introduction of the hammer into the primary circuit as in the 

 ordinary induction apparatus is inadmissible here, for if the coil of 



