THE PHENOMENON OF CONTRACTION. 45 



applying the ear or a stethoscope to the muscle. The note that 

 IS heard corresponds in pitch, up to a certain point, with the num- 

 ber of stimuli sent in, — that is, the muscle vibrates, as it were, iq 

 unison with the number of stimuli, and, although the vibrations 

 are not sufficient to affect the recording lever, they can be heard 

 as a musical note. This fact, therefore, may be taken as a proof 

 that during complete tetanus there is a discontinuous series of 

 changes in the muscle the rate of which corresponds with that of the 

 stimulation. The series of electrical changes corresponding with the 

 series of stimuli sent in may be made audible by applying i telephone 

 to the muscle. Making use of this method, Wedenski* has shown 

 that the ability of the muscle to respond isorhythmically to the 

 rate of stimulation is limited. In frog's muscle the pitch of the 

 musical tone may correspond with the rate of stimulation up to 

 about 200 stimuli per second. In the muscle of the warm-blooded 

 animal the correspondence may extend to about 1000 stimuli per 

 second. If the rate of stimulation is increased beyond these 

 limits the musical note heard does not correspond, but falls 

 to a lower pitch, indicating that some of the stimuli under these 

 conditions become ineffective. It should be added that the high 

 figures given above for the correspondence between the stimuli and 

 the muscle-tone hold good only for entirely fresh preparations. 

 The lability of the muscle quickly becomes less as it is fatigued ; so 

 that in the frog, for instance, the correspondence in long-continued 

 contractions is accurate only when the rate of stimulation does 

 not exceed 30 per second. 



The Number of Stimuli Necessary for Complete Tetanus. — 

 The number of stimuli necessary^ to produce complete tetanus 

 varies, as we should expect, with the kind of muscle used and in 

 accordance with the rapidity of the process of relaxation shown 

 by these muscles in simple contractions. The series that may be 

 arranged to demonstrate this variation is quite large, extending 

 from a supposed rate of 300 per second for insect muscle to a low 

 limit of one stimulus in 5 to 7 seconds for plain muscle. The frog's 

 muscle goes into complete tetanus with a rate of stimulation of 

 from 20 to 30 per second. Inasmuch as the rapidity of relaxation 

 of the muscle is much retarded by certain influences, such as a 

 low temperature or fatigue, it follows that these same influences 

 affect in a corresponding way the rate of stimulation necessary to 

 give complete tetanus. A frog's muscle stimulated at the rate of 

 10 stimuli per second may record an incomplete tetanus, but if the 

 stimulus is maintained for some time the tetanus finally becomes 

 complete in consequence of the slowing of the phase of relaxation, 



* Wedenski, " Du rhythme muscuiaire dans la contraction normale," 

 " Archives de physiologie," 1891, p. 58. 



