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MUSCLE-NERVE PHYSIOLOGY 



The Demonstration of Muscle Currents. The demonstration of electrical currents 

 in muscle requires a galvanometer and non-polarizing electrodes. A muscle prism is 

 insulated, and a pair of non-polarizable electrodes connected with a very delicate galva- 

 nometer, figure 322, are applied to various points of the prism; and by a deflection of the 

 needle to a greater or less extent in one direction or another, the strength and direction of 

 the currents in the piece of muscle can be determined. It is necessary to use non-polariz- 

 able and not metallic electrodes in this experiment, as otherwise there is no certainty that 

 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 cyl- 

 inder, a, drawn abruptly to a point, and fitted to a socket capable of movement, and at- 

 tached to a stand, A , so that it can be raised or lowered as required. The lower portion 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 -amalgamated 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-polarizable electrodes, it will be found that the currents 

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



FIG. 324. Diagram of the Currents in a Muscle Prism. (Du Bois -Raymond.) 



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 

 in all probability due to chemical changes going on in the muscles at the in- 

 jured ends. 



Action Currents. When a muscle is made to contract the demar- 

 cation current undergoes a sharp decrease as shown by the deflection of the 

 galvanometer needle, which swings back in the direction of equilibrium. 



