en. XT.] 



NON-rOLARTSABLE ELECTRODES 



119 



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. 

 136 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*9 per 

 cent, sodium chloride); on this pad one end of the muscle rests. 

 The binding screw (&) 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 



FIG. 136. Non-polarisable elec- 

 trode of Du Bois Reymond. 

 (M'Kendrick.) 



FIG. 137. -Diagram of Du Bois Reymond'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 physiological salt solution ; in the solution of zinc sulphate 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. 



potential (that is, difference in amount of positive or negative elec- 

 tricity) 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. 



