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A MANUAL OF VETERINARY PHYSIOLOGY 



behave in a perfectly regular manner in passing from one definite 

 point on the muscle to another. These are the so-called natural 

 muscle currents, or currents of rest ; they are found to pass in a 

 certain direction — viz., from the longitudinal surface of the 

 muscle to the cut extremity. The natural surface of the muscle, 

 therefore, corresponds to the copper of a Daniell's cell, the cut 

 ends to the zinc element ; the surface of the muscle is in conse- 

 quence galvanometrically positive, the cut ends galvanometrically 

 negative (see p. 395). The more the ends are injured the more 



Fig. 121. — Diagram illustrating the So-called Electric Currents of 

 Rest (Injury Currents) of Muscle and Nerve (Foster). 



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

 excepting that the currents at the transverse section cannot be shown in 

 a nerve. The arrows show the direction of 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, take 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 section is 

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

 by the dotted lines. 



galvanometrically negative they become. It is now known that 

 the currents of rest in muscle are caused by the injury inflicted on 

 the muscle in its course of preparation for the experiment. They 

 are in consequence frequently described as injury currents. 

 Muscle at rest and absolutely uninjured gives no current whatever. 

 If while the galvanometer is registering the direction of an 

 injury current the muscle preparation be stimulated with an inter- 

 rupted current, a backward swing of the needle of the instrument 

 towards zero indicates that the injury current is diminished ; 

 this diminution is termed the negative variation. 



