46 



ANIMAL MECHANISM. 



vibrates in the depths of its tissue under these conditions of 

 contraction, because the ear applied to this muscle hears a 

 sound whose acuteness is exactly determined by the number 

 of the electric excitations sent to the muscle in a second. 



By means of a very sensitive myograph, we have been able 

 to render visible the vibrations of the muscles under the in- 

 fluence of tetanus -producing shocks. 



Fig. 11 shows how this fusion of shocks is manifested 

 by a contraction of the muscle, permanent in appearance, but 

 in which the tracing reveals vestiges of vibrations. Vibrations 

 may be found in the tetanus which strychnine p'roduces in the 

 muscles of an animal, as well as in that which is caused by 

 the irritation of a nerve by heat and chemical agents. 



Fjg. 11 — Gradual coalescence of the shocks produced by electric excitations of 

 increasing frequency. 



In short, these voluntary contractions seem to be only a 

 series of shocks, combining together by the rapidity of their 

 succession. 



It has long been known that by applying the ear to a 

 muscle in a state of voluntary contraction, we can hear a 

 grave sound, whose tone several authors have sought to 

 determine. WoUaston, Houghton, and Dr. Collongue are 

 almost agreed upon this tone, which would correspond to a 

 frequency of 32 or 35 vibrations per second. Helmholtz 

 thinks that this tone of 32 vibrations per second is the normal 

 sound given out by the muscle in contraction, and according 

 to his experiments in electric tetanization, he regards this 



