20 



fixed to the cork by a pin. (7) Make and break the current 

 by moving the drum with the hand in one direction so as 

 not to displace the striker, and move the secondary coil out 

 till breaking alone causes a contraction. 



D. Take Trace. 



(1) Now bring the point of the lever lightl} r against the 

 smoked surface of the drum, (a) pointing it in the direction in 

 which the drum travels, (6) and taking care that the movable 

 base-piece of the frogboard is pushed thoroughly home, so that the 



FIG. 12. Muscle attached to Lever. 



lever may be swung off and on to the drum when required. 

 (2) With the finger raise the lever to see that it marks properly, 

 and if necessary adjust lever. (3) With the key in the 

 secondary circuit closed start the drum, and, when it is revolv- 

 ing steadily, open the key in the secondary circuit, so that 

 the current may reach the electrodes and nerve. When the 

 muscle is stimulated it contracts and pulls up the lever and 

 records the contraction on the drum. (4) Whenever the two 

 records are made, close the key again and stop the drum. (Don't 

 reverse the drum and don't move the stand of the frogboard.} 



E. Mark the Moment of Stimulation. 



To mark the moment of stimulation, revolve the drum 

 slowly with the hand, keeping the key in the secondary shut 

 till the striker is just about to make contact, then open the 

 key and cautiously continue the movement of the drum 

 till the muscle contracts and marks the moment of stimulation . 

 Note the relationship of this mark, which indicates the moment 

 of stimulation, to the upstroke which marks the contraction. 



F. Make a Time Trace. 



(1) Swing the lever off the paper by using the base- 

 piece (don't move the drum or the myograph stand). (2) 



