STIMULATION OF MUSCLE AND NERVE 109 



leave fibres at points other than those in contact 

 with the electrodes. 



The difference between the operator's elec- 

 trodes and the physiological anode and cathode 

 is also obvious when the electrodes are applied 

 to skin, connective tissue, mucous membrane, etc., 

 covering the muscle or nerve, the points at 

 which the electrodes touch the covering tissue 

 cannot be the points at which the current actu- 

 ally leaves or enters the muscle. 



The failure to keep this distinction in mind 

 may lead to wholly erroneous interpretations. 

 Thus when the ureter is extirpated, or is raised 

 from the tissues on which it normally rests, its 

 reaction to the galvanic current follows the law, 

 contraction begins at cathode on making, at 

 anode on breaking the current ; but when the 

 ureter is stimulated in situ, exactly the opposite 

 effect is seen, contraction begins at anode on 

 making the current. The explanation is that 

 the current lines in the latter case are very 

 widely diffused through the conducting tissues 

 on which the ureter lies, so that the current 

 passes into and out of the muscle fibres for some 

 distance either side of the positive electrode. 

 Each point at which the current leaves a fibre 

 is a secondary cathode, and if the number of 

 such points is large, cathodal stimulation will 



