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 ex ictly determined by the number 

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



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

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

 liuence of tetanus -producing shocks. 



Fig. 1 1 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 vibration*. Vibrations 

 may be found in the tetanus which strychnine produces 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. 



FIG 11. Gradual coalescence of the shocks produced by cle. trie excitations of 



iuae.ising 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. "Wollaston, Iloughton, and Dr. Collongue are 

 almost agreed upon this tone, which would correspond to a 

 frequency of ',','2 or .">"> vibrations per second. Helmholtz 

 thinks that this tone of ;'>'_' vibrations per second is the normal 

 sound given out by the muscle in contraction, and according 

 to liis i .xperimeuts in electric totalization, he regards this 



