SECTION VII 



ELECTRICAL CHANGES IN MUSCLE 



IF a current from a battery be passed between two plates of platinum 

 immersed in acidulated water or salt solution, electrolysis of the water 

 takes place, bubbles of hydrogen appearing on the positive plate 

 (anode), and bubbles of oxygen on the negative plate (cathode). 

 If now we remove the battery, and connect 

 the two plates (electrodes) by wires with a 

 galvanometer, a current passes through the 

 galvanometer and water in the reverse 

 direction to the previous battery current. 

 This current is called the polarisation current, 

 and is due to the electrolysis of the water 

 that has taken place. The vessel in which 

 the electrodes are immersed has in fact 

 FIG. 76. Diagram of non- become a galvanic cell, the platinum covered 



polarisable electrode. .,, , ,,, , . . 



a, covered wire; 6, amal- Wlth OX 7g en bubbles beln g tlie P OSltlve 



gamated zinc rod ; c, element, and that covered with hydrogen 

 lXt\on;tplugo d bubbles the negative eknxnt. Exactly the 

 zinc sulphate clay;/, plug same process of electrolysis or polarisation 



of normal saline clay. -111 ,11 



takes place when we pass currents through 

 the tissues of the body by means of metallic electrodes. 



Hence before we can study accurately the delicate electrical 

 changes that may occur normally in living tissues, it is necessary 

 to have some form of electrodes in which this polarisation will not 

 occur. The ' non-polarisable ' elec- 

 trodes which are most generally used 

 for this purpose are made in the 

 following way. A glass tube (Fig. 76) 

 is closed at one end with a plug of 

 kaolin made into a paste with a satu- 

 rated solution of zinc sulphate. The 

 rest of the tube is filled with a 

 similar solution. Dipping into the 

 zinc sulphate solution is a rod of 



pure zinc, amalgamated. Just before use, a plug of china clay 

 made with normal saline solution is put on the end of the tube, 



251 



FIG. 77. U-shaped non-polarisabh 

 electrodes. 



