332 PROTOPLASMIC ACTION AND NERVOUS ACTION 



fifty per second.^ Records taken from other muscles 

 showed similar but not always identical rates, varying 

 from forty per second in the thigh muscles to sixty per 

 second or more in the jaw muscles; and it appears 

 probable that under normal conditions different muscles 

 have characteristic differences in their electromotor 

 rhythms. There is every evidence that the muscle 

 rhythm corresponds to the electromotor rhythm of 

 innervation, which in turn corresponds to the rhythm 

 of discharge from the nerve cells in the central nervous 

 system. Numerous observations since Helmholtz' time 

 have shown that a voluntary muscle during contraction 

 emits a low musical note, apparently indicating a 

 rhythmical variation in mechanical tension; and it has 

 been shown by stimulating the nerve rhythmically, by 

 tetanizing currents of known frequency, that the note 

 derived from the muscle has a pitch corresponding with 

 the rhythm of innervation, up to a frequency of several 

 hundred per second.^* The same is true of the rhythm 

 of the electric variation obtained from the muscle 

 during rhythmical innervation; in the frog's muscle 

 the rhythmical electromotor variations show the same 

 frequency as that of the stimulus, until an upper limit 

 of about 150 to 200 per second (at room temperature) 

 is reached; above this limit the electric variations of the 

 muscle are less frequent than those of the nerve, becoming 

 irregular with the higher frequencies.^ In the case of 



^H. Piper, Elektrophysiologie menschlicher Muskeln, Berlin (19 12); 

 cf. chap. vii. 



2 Cf . Piper, op. cit., chap, x, p. 143, for a fuller account and references 

 to literature. 



3 Cf. F. Buchanan, Journal of Physiology, XXVII (1901), 95; Hoff- 

 mann, Archiv Anat. u. Physiol. (1909), p. 43°; also Judin, Arch. ges. 

 Physiol., CXCV (1922), 527. 



