482 MUSCLE-NERVE PHYSIOLOGY 



the whole of the current observed is communicated from the muscle itself 

 and not derived from the metallic electrodes and arising in consequence of the 

 action of the saline juices of the tissues upon them. The form of the non- 

 polarizable electrodes is a modification of Du Bois Reymond's apparatus, 

 figure 323, which consists of a somewhat flattened glass cylinder, a, drawn 

 abruptly to a point, and fitted to a socket capable of movement, and attached 

 to a stand, A, so that it can be raised or lowered as required. The lower por- 

 tion of the cylinder is filled with china clay moistened with saline solution, 

 part of which projects through its drawn-out point; the rest of the cylinder is 

 filled with a saturated solution of zinc sulphate into which dips a well-amal- 



FIG. 323. Diagram of Du Bois Reymond's Non-polarizable Electrodes, a, Glass 

 tube filled with a saturated solution of zinc sulphate, in the end, c, of which is china clay 

 drawn out to a point; in the solution a well-amalgamated zinc rod is immersed and con- 

 nected, by means of the wire which passes through a, with the galvanometer. The re- 

 mainder 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. 



gamated piece of zinc connected by means of a wire with the galvanometer. 

 In this way the zinc sulphate forms a homogeneous and non-polarizable 

 conductor between the zinc and the china clay. A second electrode of the 

 same kind is, of course, necessary. Recently Porter has devised a boot- 

 shaped clay electrode that is burned, and hence has the immense advantage of 

 permanency. 



Currents of Injury, or Demarcation Currents. If a segment is cut 

 out of a living gastrocnemius, its cut ends present regions of maximal injury. 

 Such a preparation is called a muscle prism. 



If the points on the surface of a muscle prism be connected with the gal- 

 vanometer by non-polorizable electrodes, it will be found that the currents 

 pass from point to point, as shown in the diagram, figure 324. 



The strongest currents pass from the equator to a point representing the 

 middle of the cut ends; currents also pass from points nearer the equator to 

 those more remote, but not from points equally distant, which are isoelectric 

 points. The cut ends are always negative to the equator. The currents are 



