58 MUSCLE CURRENTS. [BOOK i. 



with its irritability. The exhausted muscle when extended does 

 not return so readily to its proper length as the fresh active muscle, 

 and, as we shall see, the dead muscle does not return at all. 



Electrical Changes. 



Muscle-currents. If a muscle be removed in an ordinary 

 manner from the body, and two non-polarisable electrodes 1 , con- 



z.s 

 di.c 



FlG. 11. NON-POLABISABLE ELECTRODES. 



a, the glass tube; z, the amalgamated zinc slips connected with their respective 

 wires; z. s., the zinc sulphate solution; ch. c., the plug of china clay; c', the portion 

 of the china-clay plug projecting from the end of the tube; this can be moulded into 

 any required form. 



nected with a delicate galvanometer of many convolutions, be 

 placed on two points of the surface of the muscle, a deflection of 

 the galvanometer will take place indicating the existence of a 

 current passing through the galvanometer from the one point of 

 the muscle to the other, the direction and amount of the deflection 

 varying according to the position of the points. The 'muscle- 

 currents' thus revealed are seen to the best advantage when the 

 muscle chosen is a cylindrical or prismatic one with parallel fibres, 

 and when the two tendinous ends are cut off by clean incisions at 

 right angles to the long axis of the muscle. The muscle then 

 presents a (artificial) transverse section at each end and a longi- 

 tudinal surface. We may speak of the latter as being divided 

 into two equal parts by an imaginary transverse line on its surface 



1 These (Fig. 11) consist essentially of a slip of thoroughly amalgamated zinc 

 dipping into a saturated solution of zinc sulphate, which in turn is brought into 

 connection with the nerve or muscle by means of a plug or bridge of china-clay 

 moistened with normal sodium chloride solution ; it is important that the zinc should 

 be thoroughly amalgamated. This form of electrodes gives rise to less polarisation 

 than do simple platinum or copper electrodes. The clay affords a connection be- 

 tween the zinc and the tissue which neither acts on the tissue nor is acted on by the 

 tissue. Contact of any tissue with copper or platinum is in itself sufficient to de- 

 velope a current. 



