618 A MANUAL OF PHYSIOLOGY 



nerves right up to the vertebral column. Lay their upper ends on 

 electrodes and stimulate; the muscle of the ligatured limb will 

 contract. This proves that the nerve-trunks are not paralyzed by 

 curara, since the poison has been circulating in them above the 

 ligature. The muscle of the leg which was not ligatured will 

 contract if it be stimulated directly, although stimulation of its nerve 

 has no effect. The muscular fibres, accordingly, are not paralyzed. 

 The seat of paralysis must therefore be some structures physio- 

 logically intermediate between the nerve-trunk and the muscular 

 fibres (p. 551). 



8. Graphic Record of a Single Muscular Contraction or Twitch. 

 Pith a frog (brain and cord), make a muscle-nerve preparation, 

 and arrange it on the myograph plate, as in i (b). Lay the nerve on 

 electrodes connected with the secondary coil of an induction machine 

 arranged for single shocks. Introduce a short-circuiting key (Fig. 158) 

 between the electrodes and the secondary coil, and a spring key in 

 the primary circuit. Close the short-circuiting key, and then press 

 down the spring key with the finger. Let the drum off (fast speed) ; 

 the writing-point will trace a horizontal abscissa line. Open the 

 short-circuiting key, and then remove the finger from the spring-key. 

 The nerve receives an opening shock, and the muscle traces a curve. 

 Now adjust the writing-point of an electrical tuning-fork (Fig. 192), 

 vibrating, say, 100 times a second, to the drum, and take a time- 

 tracing below the muscle-curve. Stop the drum, or take off the 

 writing-point, the moment the time-tracing has completed one cir- 

 cumference of the drum, so that the trace may not run over on itself. 

 Cut off the drum-paper, write on it a brief description of the experi- 

 ment, with the time-value of each vibration of the fork, the date, 

 and the name of the maker of the tracing, and then varnish it. An 

 exactly similar tracing can be obtained by directly stimulating the 

 muscle (curarized or not). 



9. Influence of Temperature on the Muscle-curve. Pith a frog 

 (brain and cord), make a muscle-nerve preparation, and arrange it 

 on a myograph. Lay the nerve on electrodes connected through a 

 short-circuiting key with the secondary coil of an induction-machine, 

 or connect the muscle directly with the key by thin copper wires. 

 Take a Daniell cell, connect one pole through a simple key with 

 one of the upper binding-screws of the primary coil, and the other 

 pole with the metal of the drum. A wire, insulated from the 

 drum, but clamped on the vertical part of its support, and with its 

 bare end projecting so as to make contact with a strip of brass 

 fastened on the spindle, is connected with the other upper terminal 

 of the primary (Fig. 192). At each revolution of the drum the 

 primary circuit is made and broken once as the strip of brass brushes 

 the projecting end of the wire. The object of this arrangement is to 

 ensure that when the writing-point of the myograph lever has been 

 once adjusted to the drum, successive stimuli will cause contractions, 

 the curves of which all rise from the same point. Close the key in 

 the primary, set the drum off (fast speed), open the short-circuiting 

 key, and as soon as the muscle has contracted once, close it again. 



