40 PRACTICAL PHYSIOLOGY 



Attach the muscle to the lever of the myograph 

 in the usual way ; place the nerve upon the elec- 

 trodes ; describe an abscissa ; set the reed vibrat- 

 ing ; open the key in the secondary circuit for 

 about a second ; take the lever point away from 

 the drum. A tracing is to be taken in this way at 

 each of the above rates, each tracing on its own 

 abscissa ; add a time marking. 



FIG. 28. TRANSMISSION MYOGRAPH OF MAREV. F, FORCEPS FOR GRASPING THE MUS- 

 CLE THE CONTRACTION OF WHICH is TO BE RECORDED. THE Two BLADES OF THE 

 FORCEPS ARE DRAWN TOGETHER BY AN INDIA-RUBBER BAND. 7", RECEIVING TAM- 

 BOUR, THE AlR IN WHICH IS COMPRESSED BY THE SWELLING OF THE MUSCLE, AND 



FROM WHICH THE PRESSURE IS TRANSMITTED BY AN INDIA-RUBBER TUBE TO T' t 

 THE RECORDING TAMBOUR, THE LEVER OF WHICH WRITES ON A REVOLVING DRUM. 



Record of voluntary contraction. A volun- 

 tary muscular contraction, say of the finger-muscles, 

 may be recorded in the same way as the contraction 

 of a frog's muscle, by resting the hand upon the frog- 

 plate and tying a thread to one of the fingers, the 

 other end of the thread being attached to the lever ; 

 this should, however, either be furnished with a 

 moderately heavy weight or held down by a strong 

 spring or elastic band. On abducting the finger 



