178 



EXPERIMENTAL PHYSIOLOGY. 



LESSON XXXV. 



FATIGUE OF MUSCLE. 



1. Fatigue of Muscle. 



(a.) Arrange an induction apparatus for single shocks, but 

 introduce into the primary circuit in addition to the du Bois 

 key a trigger-key, the latter fixed to a stand, and so placed 

 that a tooth on the edge of the drum can knock it over, and 

 thus break the primary current as required. Or attach to 

 the edge of the under surface of the drum a short style ; a 

 strong pair of bull-dog forceps clamped on to it does 

 perfectly well. 



(6). Make a nerve-muscle preparation, clamp the femur, 



and adjust the 

 preparation in 

 the moist cham- 

 ber, or a crank- 

 myograph the 

 whole to be sup- 

 ported on a tan- 

 gent stand. At- 

 tach the muscle 



to a writing- 

 Fig. 71.-Fatigue Curve.-The sciatic nerve : was leyer to record 



a revolving 

 drum. 



stimulated with maximal induction shocks 

 and every fifteenth contraction recorded. 



(c.) Close the trigger-key, and on allowing the cylinder 

 to revolve, the style knocks it over, breaks the primary 

 circuit, and induces a shock in the secondary. Immediately 

 short-circuit the secondary circuit, close the trigger-key 

 and unshort-circuit the secondary circuit, and allow the 

 drum to revolve. Repeat this until the muscle is fatigued. 

 Record only every fifteenth contraction. In this way the 

 muscle is always stimulated at the same moment, and the 

 various curves are superposed, and can be readily com- 

 pared (Fig. 71). 



