592 



PHYSIOLOGY. 



trary to the current of rest. This negative variation can stimulate 

 the nerve of another muscle if the nerve of the physiological rheo- 

 scope be placed on the contracting muscle in such a man- 

 ner that the first touches both the cut surface and another point on 

 the muscle; then each contraction of the muscle is followed by 

 a contraction of frog's nerve-muscle preparation (secondary con- 

 traction). This negative variation lasts about 0.004 second and is 



Fig. 228. The Negative. Variation (Frog's Gastrocnemius.) 



(WALLER.) 



Simultaneous record of a tetanic contraction (white line) and of the accom- 

 panying negative variation of a current of injury (black line), (a) The Current 

 of injury is normally subsiding; (&) it is suddenly diminished during tetanus 

 (negative variation) ; (c) it subsequently increases (positive after-variation) ; and 

 (d) it finally resumes its normal decline. 



propagated along the muscle with the same velocity as the wave of 

 contraction it precedes, vanishing even before the arrival of the lat- 

 ter. Hermann calls the negative variation by the name of current 

 activity or action current. 



