ANALYSIS OF A MUSCULAR CONTRACTION. 



169 



(c.) Make a nerve-muscle preparation, fix the femur in the 

 clamp, attach the 

 tendo Achillis to 

 the writing-lever 

 (S), and place the 

 nerve over the 

 electrodes in the 

 ordinary muscle 

 moist chamber. 

 Adjust the moist 

 chamber on its 

 stand and raise it to 

 a suitable height. 

 Load the lever 

 with 20 grammes, 

 and direct its point 

 to the side to which 

 the pendulum 

 swings. Fix the 

 pendulum with the 

 detent, and adjust 



B 



Fig. 63. Scheme of the arrangement of the 

 pendulum. B, Battery ; I., primary, II., 

 secondary spiral of the induction machine; 

 S', tooth ; K', key ; C, C, catches ; K' in 

 the corner, scheme of K' ; K, key in 

 primary circuit. 



the writing - style 

 of the lever on 

 the smoked sur- 

 face. Connect the 

 secondary spiral 

 either with the 

 muscle directly, or preferably, with the electrodes on which 

 its nerve rests, introducing a short-circuiting key. In 

 Fig. 63 this is omitted, and the wires of the secondary circuit 

 go direct to the muscle. After un-short-circuiting, with 

 the hand break the primary circuit to make certain that a 

 contraction occurs on breaking the primary circuit. 



(d.) See that the trigger-key (K') of the pendulum (in the 

 primary circuit) is closed, and the key in the secondary 

 circuit open. Allow the pendulum to swing as it does so, it 

 knocks open the key in the primary circuit and breaks the 

 current, thus inducing a shock in the secondary circuit, 

 whereby the muscle is stimulated and caused to record its 

 contraction or muscle-curve on the smoked surface. 



(e.) Take the abscissa i.e., the base line. Rotate the stand 

 on which the moist chamber is supported, so as to withdraw 



