The Muscular System. 



247 



in muscle during contraction, and these are spoken of as 

 the currents of action. 



Currents of action occur during the phase of muscular 

 contraction known as the latent period, a term to be presently 

 described. These currents are not attended by any visible 

 alteration in the state of the muscles, but a contraction 

 follows as the result of their passage ; as Foster expresses 

 it : ' they prepare the way for the visible change of form 

 which is to follow.' The current of action travels with 



Fir,. 20.— Diagram Illustrating the Electric Currents of 

 Rest of Nerve and Muscle. 



Beintf 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 ot 

 the current through the galvanometer. 



a b, the equator. The strongest currents are those shown by the dark 

 ' lines, as from a at the 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 farther 

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

 circumference to a point nearer the centre of the transverse sec- 

 tion is shown at g, h. From a to b, or from x to y, there is no 

 current, as indicated by the dotted lines (Foster). 



great rapidity to the nerve termination in the muscle 

 known as the motor end plate ; a contraction now follows, 

 produced by a decomposition of the muscle substance, the 

 contraction being in the form of a visible wave, which leads 

 to swelling and shortening of the muscle fibres. 



