122 CHANGE IN FORM IN A MUSCLE WHEN IT CONTRACTS [CH. X. 



muscular tetanus,* or voluntary tetanus, as it may conveniently be 

 termed. 



If a stethoscope is placed over any contracting muscle of the 

 human body, such as the biceps, a low sound is heard. The tone of 

 this sound, which was investigated by Wollaston, and later by 

 Helmholtz, corresponds to thirty-six vibrations per second ; this was 

 regarded as the first overtone of a note of eighteen vibrations per 

 second, and for a long time 18 per second was believed to be the 

 rate of voluntary tetanus. 



The so-called " muscle sound " is, however, no indication of the 

 rate of muscular vibration. Any irregular sound of low intensity 

 will produce the same note ; it is, in fact, the natural resonance-tone 

 of the meinbrana tympani of the ear, and, therefore, selected by the 

 organ of hearing when we listen to any irregular mixture of faint, 

 low-pitched tones and noises. 



A much more certain indication of the rate of voluntary tetanus 

 is obtained by the graphic method. The myographs hitherto de- 

 scribed are obviously inapplicable to the investigation of such a 

 problem in man. The instrument employed is termed a transmis- 

 sion myograph. The next figure shows the recording part of the 

 apparatus. 



It is called a Marey's Tambour. It consists of a drum, on the 



Screw to regulate elevation of lever. 



Writing lever. 



Tambour. 



Tube to receiving 

 tambour. 



Fio. 153. Marey's Tambour, to which the movement of the column of air in the first tambour is 

 conducted by a tube, and from which it is communicated by the lever to a revolving cylinder, so 

 that the tracing of the movement is obtained. 



membrane of which is a metallic disc fastened near one end of a 

 lever, the far extremity of which carries a writing point. The interior 

 of the drum is connected by an india-rubber tube (seen at the right- 

 hand end of the drawing) to a second tambour called the receiving 

 tambour, in which the writing lever is absent. Now if the receiving 

 tambour is held in the hand, and the thumb presses on the metallic 



* The use of the word tetanus in physiology must not be confounded with 

 the disease known by the same name, in which the most marked symptom is an 

 intense condition of muscular tetanus or cramp. 



