GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



9 1 



the chemic changes underlying its nutrition, and hence their intensity 

 rises and falls with all the conditions which maintain or impair mus- 

 cle nutrition and irritability. The currents observed in the injured 

 muscle during the inactive state have been termed currents of rest. 

 du Bois-Reymond regarded them as preexistent, intimately connected 

 with the living condition of the muscle, and essential to the performance 

 of its functions, and to be explained by the view that the entire muscle 

 is composed of molecules each of which exhibits the same difference 

 of potential on its longitudinal and transverse surfaces as the muscle 

 prism itself. Hermann denies the existence of currents in normal 

 resting muscle and attributes them to injuries of the surface, due to 

 methods of preparation, in consequence of which the tissue dies and 

 becomes electronegative to the uninjured area, which remains electro- 

 positive. These currents Hermann terms "demarcation currents." 



Negative Variation of the Muscle Current. If a muscle 

 exhibiting a current of injury be excited to activity by tetanizing in- 

 duced currents applied to 

 the opposite end of the 

 muscle, it will be ob- 

 served that as the con- 

 traction wave passes over 

 the muscle there is a 

 movement of the galvan- 

 ometer needle toward the 

 zero point, indicating a 

 diminution of the poten- 

 tial on the longitudinal 

 surface. To this dimi- 

 nution 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 position. The diminution 

 of potential on the longitudinal surface of the muscle is now 

 attributed to the passage of the excitation and contraction pro- 

 cesses, to a temporary disintegration of the muscle substance (Fig. 

 35). With their disappearance and the subsequent restoration of 

 the nutrition of the muscle, the former electric condition returns. 



The primary deflection of the galvanometer needle is due to the 

 demarcation current which arises as a result of the difference in 

 electric potential produced by the 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. 



FIG. 35. THE NEGATIVE VARIATION OF THE DE- 

 MARCATION CURRENT. A. The contraction 

 wave, which as it passes beneath the electrode 

 at B causes a diminution of potential. 



