ELECTROTONUS. 



127 



conducted ; by means of proper apparatus the current 

 may be strengthened or weakened, and may be closed 

 and interrupted by means of a key at s. Let a current 

 from a sliding inductive apparatus pass through another 

 portion of the nerve, e.g. a 6, and let us find that posi- 

 tion of the secondary coil at which the muscle exhibits 

 marked pulsations of medium strength. The changes 

 which occur in these pulsations when the current in 

 the portion c d is alternately closed and interrupted 



FIG. 30. ELECTROTOXUS. 



must now be observed. It is found that these changes 

 depend on the direction of the current within the nerve. 

 If the current passes in the direction from c to d, then 

 the action of the same irritant is weakened in the por- 

 tion a b as soon as the current is closed, but regains its 

 former strength as soon as the current is' interrupted. 

 In this case, therefore, the excitability in the contiguous 

 portion a b was lowered or hindered by the influence 

 of the constant current traversing the portion c d. If, 

 however, the constant current is reversed, so that it 



