CH. X.] 



VOLUNTARY TETANUS. 



129 



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 described are obviously inapplicable to the investigation 

 of such a problem in man. The instrument employed is termed 

 a transmission 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 

 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 



Screw to regulate elevation of lever. 



Writing lever. 



Tambour. 



Tube to receiving 

 tambour. 



Kg. 153. Marey's Tambour, to which the movement of the column of air in the flrbt 

 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. 



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 disc on the surface of its membrane, the 

 air within it is set into vibrations of the same rate as those 

 occurring in the thumb muscles ; and these are propagated to 

 the recording tambour and are written in a magnified form by 

 the end of the lever on a recording travelling surface. 



The tracing obtained is very like that in fig. 151 ; it is an 

 incomplete tetanus, which by a time marker can be seen to be 

 made up of i o to 12 vibrations a second. 



In some diseases these tremors are much increased, as in the 

 clonic convulsions of epilepsy, or those produced by strychnine 

 poisoning, but the rate is the same. 



Similar tracings can be obtained in animals by strapping the 



receiving tambour on the surface of a muscle, and causing it to 



contract by stimulating the brain or spinal cord. The rate 



of stimulation makes no difference ; however slow or fast the 



K.P. K 



