242 PHYSIOLOGY 



by him to give a typical diphasic variation in the muscles. When the 

 muscles were contracted voluntarily, well-marked oscillations of the galvano- 

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

 eight to fifty complete diphasic variations in the second (Fig. 93). Piper 

 obtained similar records on leading off 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 



FIG. 93. Electrical variations produced by voluntary contractions of 

 human muscle. (PIPER.) 



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. Dittler 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 each contraction is a fused series of single contractions, 

 evoked by the discharge along the nerve of between fifty and seventy 

 excitations per second. So far therefore the evidence is in favour of the 

 view that voluntary contraction, and, one must add, the tonic contractions 

 of all skeletal muscles, are discontinuous in nature and analogous to the 

 tetanus which we may evoke artificially by rapid stimulation either of 

 muscle or of its motor nerve. 



