PRACTICAL PHYSIOLOGY 41 



the lever is raised, and a curve is described which 

 bears a close resemblance to a tetanus produced 

 by ten or twelve vibrations per second. 



Another method of obtaining such a curve is by 

 the use of the transmission myograph (Fig. 28), 

 which consists of two tambours connected by india- 

 rubber tubing. The first or receiving tambour is 

 so arranged against the muscles of the ball of the 

 thumb that when these muscles are made to con- 

 tract voluntarily the air within it is compressed, 

 and the differences of pressure are transmitted to 

 the second or recording tambour, which writes 

 against the revolving drum. 



Sound of a voluntarily contracting muscle. 

 Place the tips of the middle fingers in the ears, 

 and contract the muscles of the arm strongly. A 

 rumbling sound is heard which is generally as- 

 sumed to be caused by the successive contractions 

 of the fibres, and to indicate the rate of vibration 

 of the voluntary tetanus. The sound heard is, 

 however, probably a harmonic of the actual note 

 produced, the perception of notes of so low a pitch 

 being modified by resonance within the ear. 



