GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 81 



axis of the transverse surface have an electromotive force in the frog muscle 

 of from 0.037 to 0.075 of a Daniell cell. 



The electric currents in the muscle are intimately associated with the 

 chemic changes underlying its nutrition, and hence their intensity rises and 

 falls with all the conditions which maintain or impair muscle nutrition and 

 irritability. The currents observed in the injured muscle during the in- 

 active state have been termed currents of rest. Du Bois-Reymond regarded 

 them as pre-existent, 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 cur- 

 rents in normal resting muscle and attributes them to injuries of the sur- 

 face, 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 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. 35). 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. 35. THE NEGATIVE VARIATION OF THE 

 as a result of the difference in DEMARCATION CURRENT A. The contraction 



, wave, which as it passes beneath the electrode at 



electric potential produced by the B causes 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. 



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