136 



THE ELECTRICAL PHENOMENA OF MUSCLE [CH. XII. 



with a muscle by wires which touch the muscle, electrical currents 

 are obtained in the circuit which are set up by the contact of metal 

 with muscle. The currents so obtained form no evidence of electro- 

 motive force in the muscle itself. It is 

 therefore necessary that the wires from the 

 galvanometer should have interposed be- 

 tween them and the muscle some form of 

 electrodes which are non-polarisable. Fig. 

 163 shows one of the earliest non-polaris- 

 able electrodes of Du Bois Eeymond. It 

 consists of a zinc trough on a vulcanite base. 

 The inner surface of the trough is amalga- 

 mated and nearly filled with a saturated so- 

 lution of zinc sulphate. In the trough is 

 placed a cushion of blotting-paper, which 

 projects over the edge of the trough; on it there is a pad of china 

 clay or kaolin, moistened with physiological salt solution (0'8 per 

 cent. NaCl); on this pad one end of the muscle rests. The binding 

 screw (k) connects the instrument to the galvanometer; the other 

 end, or some other part of the same muscle, is connected by another 

 non-polarisable electrode in the same way to the other side of the 

 galvanometer. If there is any electrical difference of potential (that 



FIG. 163. Non-polarisable elec- 

 trode of Du Bois Reymond. 

 (M'Kendrick.) 



FIG. 164. Diagram of Du Bois Raymond's non-polarisable electrodes, a, glass tube filled with a satu- 

 rated solution of zinc sulphate, in the end, c, of which is china clay drawn out to a point ; the clay 

 is moistened with 0'8 NaCl solution ; in the solution a well amalgamated zinc rod is immersed and 

 connected, by means of the wire A, with the galvanometer. The remainder of the apparatus is 

 simply for convenience of application. The muscle and the end of the second electrode are to the 

 right of the figure. 



is, difference in amount of positive or negative electricity) between 

 the two parts of the muscle thus led off, there will be a swing of the 

 galvanometer needle; the galvanometer detects the existence and 

 direction of any current that occurs. 



