706 A MANUAL OF PHYSIOLOGY 



now be moved more quickly than before, unless the salt solution has 

 been so hot as to injure the cilia. 



4. Direct Excitability of Muscle Action of Curara. Pith the 

 brain of a frog, and prevent bleeding by inserting a piece of match. 

 Expose the sciatic nerve in the thigh on one side. Carefully separate 

 it, for a length of half an inch, from the tissues in which it lies. Pass 

 a strong thread under the nerve, and tie it tightly round the limb, 

 excluding the nerve. Now inject into the dorsal or ventral lymph- 

 sac a few drops of a i per cent, curara solution. As soon as paralysis 

 is complete, make two muscle-nerve preparations, isolating the 

 sciatic 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 ordinary contractile substance of the muscular fibres, 

 accordingly, is not paralyzed. The seat of paralysis must therefore 

 be some structure or substance physiologically intermediate between 

 the nerve-trunk and the general contractile substance of the muscular 

 fibres (p. 634). 



5. 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. 215, 

 p. 626) 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. 261), 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 circumference 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 experiment, 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) . 



6. 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. 261). 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 



