50 HUMAN PHYSIOLOGY 



practically fused, and hence the influence of the anode and 

 cathode, or of closing and opening, need not be considered. 

 (Practical Physiology, Chap. II.) 



It must, of course, be remembered, that the opening of 

 the primary circuit produces a more powerful current in the 

 secondary coil, and therefore a more powerful stimulation of 

 the muscle than the closure of the primary circuit (Fig. 18). 



When the galvanic current is used to stimulate muscles 

 through the skin in man or in other living animals, the 

 different action of the two poles is not so marked as in the 



Cathode Anode 



Skin 



Muscle 





FlO. 19. Electrical Stimulation of human muscle or nerve to show the passage of 

 the current across the structure, and the consequent combination of effects 

 under each pole. 



excised muscle of the frog, because the current, passing 

 through the skin above the muscle to enter the body, flows 

 not along but rather across the muscle, and thus, under each 

 pole applied to the skin there is on one side of the muscle 

 the effect of an entering current anode and on the other, 

 of a leaving current -cathode (Fig. 19). Thus the same bit 

 of muscle or nerve is subjected to anelectrotonus on one 

 side and cathelectrotonus on the other, and the effects of 

 closing and of opening therefore tend to be combined. 

 Hence with a strong current contraction occurs both on 

 closing and on opening at both poles, but as the current 

 is weakened first the contraction at the cathode on opening, 

 next at the anode on opening, then at the anode on closing, 



