CHANGES IN A MUSCLE DURING CONTRACTION. 



93 



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

 the deflection is of such a kind as to show that positive currents are con- 

 tinually 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 cur- 

 rents outside the muscle may be considered as completed by currents in the 

 muscle from the cut end to the equator. In the diagram, Fig. 30, the arrows 



FIG. 30. 



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 shown in a nerve. The arrows show the direction of the current through the 

 galvanometer. 



ab, the equator. The strongest currents are those shown 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 

 shown by the arrows, have the same direction. A current is shown from e, which is near the 

 equator, to /, which is further from the equator. The current (in muscle) from a point in the cir- 

 cumference to a point nearer the centre of the transverse section is shown at gh. From a to b, or 

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



indicate the direction of the currents. If 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 con- 

 tinues 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 (c and /), one on either side of the equator, there will be 

 a feeble current from the one nearer the equator to the one further 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 will be a current 

 through the galvanometer from the former to the latter ; there will be a cur- 

 rent of similar direction, but of less intensity, when one electrode is at the 

 circumference (<?) of the transverse section and the other at some point (7i) 

 nearer the centre of the transverse section. In fact, the points which are 

 relatively most positive and most negative to each other are points on the 

 equator and the two centres of the transverse sections ; and the intensity of 

 the current between any two points will depend on the respective distances 

 of those points from the equator and from the centre of the transverse 

 section. 



