THE ELECTROMOTIVE PHENOMENA 311 



in the opposite direction. The action current 

 passes over the heart from base to apex. 



These experiments show not only that there 

 is an action current at each systole of the heart, 

 but are evidence also that the resting heart 

 muscle is iso- electric (i. e. of uniform potential). 



The Action Current precedes the Contraction. 

 Expose the heart. Fasten a very fine copper wire 

 to the ventricle; the end of the wire may be 

 thrust through the tip of the ventricle. Mount 



Fig. 53. The Heart Lever. 



the heart lever (Fig. 53) on a stand so that the 

 writing point will write on the smoked paper of 

 the kymograph. Bring the free end of the wire 

 to the heart lever, on which it may be fastened 

 with a drop of colophonium cement. Make a 

 nerve-rnuscle preparation. Fasten the femur in 

 the upper side of the muscle clamp, at right 

 angles to the long axis of the clamp. Bring the 

 latter near the heart lever, so that the nerve may 

 rest on the ventricle. Fasten the tendon Achilles 

 to the muscle lever by a thread which passes over 

 the pulley on the axis of the lever before being 



