VOLUNTARY CONTRACTION 269 



question by recording the electrical changes accompanying the 

 natural contractions of a muscle, i.e. those excited reflexly from 

 the central nervous system. It was long ago shown by Loven that 

 a certain discontinuity could be seen in records of the electrical changes 

 obtained from a frog's muscle in the tetanic spasms produced by 

 an injection of strychnine, but according to Burdon Sanderson this 

 discontinuity represents a series of spasms discharged from the central 

 nervous system. Each discharge produces, not a twitch, but a con- 

 tinued contraction of short duration. On photographing the electrical 

 changes of strychnine spasm as obtained by a capillary electrometer, 

 he found that each individual spasm could only be compared to a 

 short tetanus. The most recent investigations of the question we 



FIG. 94. Electrical variations produced by voluntary contractions of 

 human muscle. (PIPER). 



owe to Piper, who made use of the string galvanometer, an instru- 

 ment much more delicate in the reproduction of rapid changes than 

 is the capillary electrometer. Piper led off two points in the fore-arm, 

 one electrode being placed about two inches below the bend of the 

 elbow, and the other about four inches above the wrist. A single 

 stimulus of the median nerve was found by him to give a typical 

 diphasic variation in the muscles. When the muscles Were con- 

 tracted voluntarily, well-marked oscillations of the galvanometer 

 wire were obtained, indicating the existence in the muscle of forty- 

 eight to fifty complete diphasic variations in the second (Fig. 94). Piper 

 obtained similar records on leading ofl; other muscles of the body 

 when these were placed voluntarily in a state of contraction, and he 

 concludes therefore that each voluntary contraction, short or long, 

 is a tetanus composed of about fifty fused twitches per second. These 

 results Would indicate that the impulse, which normally travels down 

 the motor nerve from the anterior cornual cell to the muscle, is 

 discontinuous, and therefore that on leading off a motor nerve to 

 a galvanometer we ought to ^obtain electrical oscillations of fifty 

 distinct stimuli per 'second. 1 [This matter has been taken up by 

 Dittler, who has investigated by means of the string galvanometer 

 the electrical changes accompanying the ordinary contractions of 

 the diaphragm, and also those occurring in the phrenic nerve. He 

 finds that both in the muscle and in the nerve there is evidence that 



