GENEKAL PHYSIOLOGY OF MUSCLE 



In studying the current of action developed by stimulation 

 it is best to employ an intact muscle with no current of rest, 

 for as this would pass in the opposite direction, it would be 

 unfavourable to the demonstration of the action current, which 

 would then seem to be only the negative variation of the current 

 of rest. When the galvanometer electrodes are applied to both 

 ends of an intact and freshly excised muscle, as in Fig. 54, A, B, 

 and the muscle is stimulated at C by an induction shock, the 

 reaction does not take place simultaneously all over the muscle, 

 but it is propagated, as we saw above (Fig. 16, p. 23), like a wave 

 from the point stimulated to the more distant points. So that 

 the end A of the muscle which is near the point of application of 



FIG. 54. Apparatus for study of diphasic 

 action current. 



Fio. 55. Myogram of a contraction of frog's gastro- 

 cnemius, TO TO, and simultaneous photograph of 

 diphasic electrical variation, e e. (A. D. Waller.) 



the stimulus C will be thrown into activity first, and the end B 

 last. Since the active points of the muscle become galvano- 

 metrically negative to the inactive points, the galvanometer needle 

 reacts in a diphasic oscillation. In the first phase A will be 

 negative to B, in the second phase B will be negative to A. The 

 first phase coincides with the transmission of the contractile wave 

 from A to B ; the second phase coincides with the contraction of 

 B, as A begins to relax. The slower the transmission of the 

 wave along the muscle, the more prolonged will be the negativity 

 of A at the beginning, and of B at the close of the contraction. 

 Hence the diphasic variation of the action current is more easily 

 demonstrated on the frog's heart, where the systolic wave is 

 propagated on an average at O'l m. per second, than in skeletal 

 muscle, where the wave of contraction is propagated at about 

 1 m. per second. 



Fig. 55 gives the myogram of a contraction produced in the 

 frog's gastrocnemius when an induction shock is sent through 



