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TEXT-BOOK OF PHYSIOLOGY 



the longitudinal surface, thence through the galvanometer to the transverse 

 surface. The longitudinal surface is, therefore, electropositive, the trans- 

 verse surface electronegative. The two points exhibiting the greatest 

 difference of potential, and hence the most powerful current, lie in the 

 equator and in the center of the transverse surface. Currents of gradually 

 diminishing intensity are obtained when the electrode placed on the longi- 

 tudinal surface is removed toward either end. Feeble currents are developed 

 when two points situated at unequal distances, either on corresponding or 

 opposite sides of the equator, are connected; in either case the current 

 flows from the point lying nearest the equator to the point farthest from it. 



Similar currents are obtained when two points 

 on the cross-section situated at unequal dis- 

 tances from the central axis are connected, 

 in which case the direction of the currents will 

 be from the point lying nearest the periphery 

 toward the center. On the contrary, no cur- 

 rent is developed when two points on the longi- 

 tudinal surface equally distant from the equa- 

 tor, or two points on the transverse surface 

 equally distant from the central axis, are con- 

 nected. Such points are said to be isoelectric. 

 These facts are shown in Fig. 3 5 . The natural 

 ends of the muscle, enclosed by sarcolemma 

 and tendon, do not exhibit, if carefully pre- 

 served from injury, the negativity characteris- 

 tic of the artificial transverse ends. 



Similar electric conditions are exhibited by 

 the muscles of man and other mammals, by 

 the muscles of birds, .reptiles, amphibia, etc. 

 The currents developed by connecting the 

 equator on the longitudinal surface with the 

 axis of the transverse surface have an electro- 

 motive 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 in- 



FIG. 35. DIAGRAM TO ILLUS- 

 TRATE THE CURRENT IN MUSCLE. 

 The arrowheads indicate the direc- 

 tion; the thickness of the lines in- 

 dicates the strength of the currents. 

 (Landois and Stirling.} 



tensity rises and falls with all the conditions which maintain or impair 

 muscle 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 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 com- 

 posed 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 electropositive. These currents Hermann 

 terms "demarcation currents." 



