82 TEXT-BOOK OF PHYSIOLOGY 



Action Currents. When two isoelectric points on the longitudinal 

 surface of a muscle are connected with a galvanometer and a single stimulus 

 applied directly to one extremity, it can be shown that as the contraction 

 wave passes beneath A, Fig. 36, the muscle-tissue at that point becomes 

 electronegative toward B and a current at once passes through the galvan- 



FIG. 36. THE CONDITION LEADING TO THE DEVELOPMENT OF THE FIRST ACTION 



CURRENT. 



ometer from B to A, as shown by the deflection of the needle toward A. As 

 the contraction wave passes beneath B it in turn becomes electronegative, 

 and a temporary condition of equal potential is established when the needle 

 returns to the zero point. In a very short time the nutrition of A is restored 



I FIG. 37. THE CONDITION LEADING TO THE DEVELOPMENT OP THE SECOND ACTION 



CURRENT. 



and becomes electropositive toward B, when a current will pass through the 

 galvanometer in the opposite direction from A to B, as shown by the move- 

 ment of the needle toward B, Fig. 37. As the contraction wave passes 

 beyond B its nutrition is restored and becomes of equal potential with A. 



