9 2 



TEXT-BOOK OF PHYSIOLOGY. 



Electric Currents from Non-injured Muscles. Though per- 

 fectly normal resting muscle, according to Hermann, is isoelectric, 

 nevertheless electric currents are developed during activity to which 

 he has given the term action currents, and which are attributed to 

 the propagation of the contraction wave. 



Action Currents. When two isoelectric points on the longitu- 

 dinal 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 cur- 

 rent at once passes through the galvanometer from B to A, as 

 shown by the deflection of the needle toward A. As the con- 

 traction wave passes beneath B it in turn becomes electronegative, 



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



CURRENT. 



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 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 movement 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. ^ The term phasic is applied to 

 these currents.^ The first current flows in the muscle in the direction 

 of progress of the contraction wave first phase ; the second current 

 flows in the reverse direction second phase; the current is therefore 

 diphasic. When a muscle is tetanized, there is but a single current 

 observed, which, however, endures so long as the tetanic contrac- 



