EFFECT OF STIMULI UPON A MUSCLE-NERVE PREPARATION 37 



depends upon its length, which can be varied by clamping it at differ- 

 ent places ; it is marked at points for producing vibrations of ten, 

 fifteen, twenty, and thirty per second (fig. 37). The secondary coil 

 should be placed at such a distance from the primary that only the 

 break shock is effective. The drum should revolve at moderate 

 speed (one revolution in ten seconds). 



Attach the muscle to the lever of the myograph in the usual way ; 

 place the nerve upon the electrodes ; set the drum revolving and 

 bring the lever point against it, using the stop ; set the reed vibrating ; 

 open the key in the secondary circuit for about a second ; take the 



PIG. 37. EXPERIMENT TO INVESTIGATE THE GENESIS OP TETANUS. a, FLAT STEEL SPRING 

 MARKED AT INTERVALS WITH THE NUMBER OP VIBRATIONS CORRESPONDING TO CERTAIN LENGTHS 



OP THE SPRING ; 6, MERCURY CUP INTO AND OUT OP WHICH A PLATINUM WIRE ATTACHED TO THE 

 SPRING DIPS. 



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. 



Record of voluntary contraction. A voluntary muscular contrac- 

 tion of the finger-muscles may be recorded by resting the hand across 

 the myograph plate and tying a thread to the abducted forefinger, 

 the other end of the thread being attached to the short arm of the 

 lever ; this is to be held down by a heavy weight or thick elastic band. 

 On adducting the finger the lever is raised, and a curve is described 

 on the moving drum which bears a close resemblance to an incomplete 

 and somewhat irregular tetanus produced by ten or twelve stimula- 

 tions per second. 



