CHAP, ir.] 



THE CONTRACTILE TISSUES. 



99 



The greatest deflection is observed when one electrode is placed 

 at the mid-point or equator of the muscle, and the other at either 

 cut end ; and the deflection is of such a kind as to shew that posi- 

 tive currents are continually passing from the equator through the 

 galvanometer to the cut end ; that is to say, the cut end is negative 

 relatively to the equator. The currents outside the muscle may be 

 considered as completed by currents in the muscle from the cut end 

 to the equator. In the diagram Fig. 19, the arrows indicate the 



FIG. 19. DIAGRAM ILLUSTRATING THE ELECTRIC CURRENTS OF NERVE AND MUSCLE. 



Being purely diagrammatic, it may serve for a piece either of nerve or of muscle, 

 except that the currents at the transverse section cannot be shewn in a nerve. The 

 arrows shew the direction of the current through the galvanometer. 



ab the equator. The strongest currents are those shewn by the dark lines, as 

 from a, at equator, to x or to y at the cut ends. The current from a to c is weaker 

 than from a to y, though both, as shewn by the arrows, have the same direction. A 

 current is shewn from e, which is near the equator, to/, which is farther from the 

 equator. The current (in muscle) from a point in the circumference to a point 

 nearer the centre of the transverse section is shewn at gh. From a to 6 or from 

 x to y there is no current, as indicated by the dotted lines. 



direction of the currents. If the one electrode be placed at the 

 equator ab, the effect is the same at whichever of the two cut ends x 

 or y the other is placed. If, one electrode remaining at the equator, 

 the other be shifted from the cut end to a spot c nearer to the 

 equator, the current continues to have the same direction, but is of 

 less intensity in proportion to the nearness of the electrodes to each 

 other. If the two electrodes be placed at unequal distances e and /, 

 one on either side of the equator, there will be a feeble current from 

 the one nearer the equator to the one farther off, and the current 

 will be the feebler, the more nearly they are equidistant from the 

 equator. If they are quite equidistant, as, for instance, when one is 

 placed on one cut end x, and the other on the other cut end y, there 

 will be no current at all. 



If one electrode be placed at the circumference of the transverse 

 section and the other at the centre of the transverse section, there 



