62 4 



A MANUAL OF PHYSIOLOGY 



with the electrical tuning-fork. (For specimen curve see Fig. 179, 



P- 57I-) 



19. Composition of Tetanus. (a) Adjust a muscle-nerve prepara- 

 tion on a myograph plate, the nerve being laid on electrodes con- 

 nected through a short-circuiting key with the secondary of an induc- 

 tion machine, the primary circuit of which contains a Daniell cell 

 and is arranged for an interrupted current (Fig. 65, p. 175). The 

 lever should be shorter than that used for the previous experiments, 

 or the thread should be tied in a hole farther from the axis of rota- 

 tion, so as to give less magnification of the contraction. Set the 

 Neef's hammer going, let the drum revolve (slow speed), and open 

 the key in the secondary. The writing-point at once rises, and traces 

 a horizontal or perhaps slightly-ascending line. Close the short- 

 circuiting key, and the lever sinks down again to the abscissa line. 

 If it does not quite return, it should be loaded with a small weight. 

 This is an example of complete tetanus. 



(b) Connect the spring shown in Fig. 194 with one of the upper 

 terminals of the primary coil, and the mercury cup with the other. 



Fasten the end 

 of the spring in 

 one of the 

 notches in the 

 upright piece of 

 wood by means 

 of a wedge, so 

 that its whole 

 length can be 

 made to vibrate. 

 Let the drum off, 

 set the spring 

 vibrating by de- 

 pressing it with 

 the finger, then 

 open the key in 

 the secondary. 

 The muscle is 

 thrown into in- 

 complete tetanus, 

 and the writing- 

 point traces a wavy curve at a higher level than the abscissa line. Close 

 the short-circuiting key, and the lever falls to the horizontal. Repeat 

 the experiment with the spring fastened, so that only f, , J, -J of its 

 length is free to vibrate. The rate of interruption of the primary 

 circuit increases in proportion to the shortening of the spring, and 

 the tetanus becomes more and more complete till ultimately the 

 writing-point marks an unbroken straight line. Put on a time-tracing 

 by means of an electro-magnetic marker connected with a metronome 

 beating seconds or half-seconds (Fig. 60, p. 170). (For specimen 

 curves see Fig. 180, p. 572.) 



19. Velocity of the Nerve -impulse. Use the spring myograph 



FIG. 194. ARRANGEMENT FOR TETANUS. 



A, upright with notches, in which the spring S is fastened 

 (shown in section) ; C, horizontal board to which A is attached, 

 and in a groove in which the mercury-cup E slides. The primary 

 coil P is connected with E, and through a simple key, K, with 

 the battery B, the other pole of which is connected with the end 

 of the spring. The wires from the secondary coil, P', go to a 

 short-circuiting key, K', from which the wires F go off to the 

 electrodes. 



