98 THERMAL CHANGES. [BOOK i. 



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

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

 nected with a delicate galvanometer of many convolutions and 



z.s 



c/t.c 



FIG. 18. NON-POLARISABLE 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. 



high resistance, 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 transverse section (artificial) at each 

 end, and a longitudinal surface. We may speak of the latter as 

 being divided into two equal parts by an imaginary transverse line 

 on its surface called the ' equator,' containing all the points of the 

 surface midway between the two ends. Fig. 19 is a diagrammatic 

 representation of such a muscle, the line ab being the equator. In 

 such a muscle the development of the muscle-currents is found to 

 be as follows. 



1 These (Fig. 18) 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 

 develope a current. 



