GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 81 



Negative Variation of the Muscle Current. If a muscle exhibiting a 

 current of injury be excited to activity by tetanizing induced currents 

 applied to the opposite end of the muscle, it will be observed that as the 

 contraction wave passes over the muscle there is a movement of the gal- 

 vanometer needle toward the zero point, indicating a diminution of the 

 potential on the longitudinal surface. To this diminution in the strength 

 of the current the term negative variation was given. On the withdrawal 

 of the stimulus the needle again returns in a short time to its former posi- 

 tion. The diminution of potential on the longitudinal surface of the muscle 

 is now attributed to the passage of 

 the excitation and contraction 

 processes, to a temporary disinte- 

 gration of the muscle substance 

 (Fig. 36). With their disappear- 

 ance and the subsequent restora- 

 tion of the nutrition of the mus- 

 cle, the former electric condition 

 returns. 



The primary deflection of the 

 galvanometer needle is due to the 

 demarcation current which arises FIG. 36. THE NEGATIVE VARIATION OF THE 



QC Q recruit rf tViP HifFpTPnrA in DEMARCATION CURRENT. A. The contraction 

 a f a / e r . enCG I 11 wave, which as it passes beneath the electrode at B 



electric potential produced by the cau ses a diminution of potential. 



destructive chemic changes taking 



place at the cut end of the muscle. The negative variation is caused by the 

 fact that the activity of the muscle, with its attendant chemic changes, will 

 always be greater in the uninjured equatorial region, and hence will always 

 tend to counterbalance the original source of difference in electric potential. 



Electric Currents from Non-injured Muscles. Though perfectly 

 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 contrac- 

 tion wave. 



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. 37, the muscle- tissue at that point becomes 

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

 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 

 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. 38. 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 ir 

 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 



