NERVE MUSCLE PREPARATION 25 



knee. Cut away most of the muscles just above the 

 knee without injuring the nerve, and with strong scissors 

 cut through the leg just above and just below the knee. 



Thrust a pin through the knee-joint between the 

 bones, and put the pin in the hole in the muscle chamber 

 (Fig. 10). Unclamp the screw at E, slide forward the 

 brass carrying the lever, and pass the loop attached to 

 the tendon of the muscle over the hook on F\ pull back 

 the brass piece till the muscle is lightly stretched and 

 the lever is horizontal. Place the nerve over the ends 

 of the electrodes //, H, and pour in Ringer's fluid to 

 cover the muscle. Hook a 10 gram weight in the hole 

 in the lever next the axle. In this position the load on 

 the muscle is 2 grams. 



Bring the lever to mark on the revolving cylinder, ad- 

 justing it so that it presses very lightly on the smoked 

 paper. Place the index of the secondary coil at 10. 



With the key in the secondary circuit shut, let the 

 drum revolve once and obtain a base line. Arrange the 

 belt on the pulleys so as to give a slow speed ; turn the 

 pulleys by hand till the bar a (Fig. 7) is a couple of 

 inches past the knock-down key, close the knock-down 

 key. Open the secondary circuit key, and let the drum 

 revolve; stop the drum as soon as it has passed the 

 knock -down key. 



Without shifting the position of the lever, take four 

 similar tracings with increasing speed of drum, the last 

 being the maximum speed. 



3. Latent period. Lower the drum so as to bring 

 the writing point above the previous tracing. Take a 

 tracing with the maximum speed of the drum ; close the 



