ELECTRIC PHENOMENA OF MUSCLE. 449 



the following plan : Some innocuous material moistened in saline 

 solution (.65 per cent.) is brought into direct contact with the 

 muscle, and, by means of saturated solution of zinc sulphate, 

 into electrical connection with amalgamated zinc terminals from 

 the galvanometer. Thus the muscle is Dot injured, and the zinc 

 solution prevents the metal terminals from producing adventitious 

 currents. 



Small glass tubes drawn to a point, the opening of which is 

 plugged with moist china clay, make a^uitable receptacle for the 

 zinc solution, or, instead of the china clay, a camel's-hair brush 

 set in plaster-of-Paris may be used to keep the zinc solution in 

 the tube, and the hair moistened in salt solution forms a suitable 

 point of contact with the muscle. If a pair of such electrodes be 

 applied to the middle of the longitudinal surface at (e) (Fig. 182), 

 and of the transverse surface at (p) respectively, and then be 

 brought into connection with a delicate galvanometer, it is found 

 that a current passes through the galvanometer from the longi- 

 tudinal to the transverse surface. A current in this direction can 

 be detected in any piece of muscle, no matter how much it be 

 divided longitudinally, and probably would be found in a single 

 fibre had we the means of examining it. The nearer to the centre 

 of the longitudinal and transverse sections the electrodes are 

 placed, the stronger will be the current received by them. If 

 both the electrodes be placed on the longitudinal or on the trans- 

 verse surfaces, a current will pass through the galvanometer from 

 that electrode nearer the middle of the longitudinal section (called 

 the equator of the muscle cylinder) to the electrode nearer the 

 centre of the transverse section (pole of muscle cylinder). If the 

 electrodes be placed equidistant from the poles or from the equator, 

 no current can be detected. 



The central part of the longitudinal surface of a piece of 

 muscle is then positive, compared with the central part of the 

 extremities or transverse sections. And between these parts, the 

 equator and poles of the muscle cylinder, where the difference is 

 most marked, are various gradations, so that any point near the 

 equator is positive when compared with one near the poles. 



There is, then, a current passing through the substance of the 

 38 



