The Nervous System. 



257 



nerve. A shock is now sent into the nerve from an induc- 

 tion coil at a place between the muscle and the continuous 

 current ; as the result of the stimulation the muscle either 

 responds more than it should do for the strength of the 

 stimulus employed, viz., there is increased excitability of 

 the nerve (kathelectrotonus), or the muscle does not 



Fig. 23.— Diagram of Electrotonus. 

 n, the nerve running to the muscle M ; E, an element for the production 

 of a constant current, the positive pole or anode (a) in a being 

 placed furthest from the muscle, the current consequently flow- 

 ing down the nerve, and in i: being placed nearest to the muscle, 

 the current flowing up the nerve ; at s the nerve is stimulated 

 by an induced current, and its irritability determined by the con- 

 traction of the muscle M ; the irritability is increased in a, 

 kathelectrotonus, and decreased in B, anelectrotonus. 



respond as strongly as it should, viz., there is decreased 

 excitability of the nerve (anelectrotonus). The increase or 

 decrease of excitability in the nerve depends upon whether 

 the continuous current is passed down it, as in Fig. A, or 

 up it, as in B ; with a descending current the excitability 

 is increased, with an ascending one it is decreased. 



17 



