THE TISSUES 47 



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 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 leavin 

 current kathode (fig. 18). Thus the same bit of muscle or 

 nerve is subjected to anelectrotonus on one side and katelectro- 

 tonus on the other, and the effects of the two poles, and there- 



Kathodfi 



i Skin 



FIG. 18. 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. M, making or closing the current ; B, opening or 

 breaking the current. W, weak ; M, medium ; , strong current. 



fore of closing and of opening, tend to be combined, although 

 the influence of, the pole placed immediately above the muscle 

 predominates. Hence with a strong current contraction occurs 

 both on closing and on opening at both poles. As the current 

 is weakened, the contraction at the kathode on opening first 

 disappears, because the anode is not predominant. Next, con- 

 traction at the anode on opening disappears because the anodal 

 stimulation is so much weaker than the kathodal. Then, the 

 contraction at the anode on closing goes because the kathode 

 is not predominating; and, finally, the contraction at the 

 kathode on closing also disappears. When the muscle is in 



