NERVE 



63 



be stated — the nerve is always stimulated at the j^oint 

 where the current leaves it. On makinof this is at the 

 cathode; on breaking at the anode (fig. 23) (Practical 

 Physiology). 



These results may be summarised as follows : — 



1. Stimulation on closing (making); stimulation on open- 

 ing (breaking). 



2. Closing stimulation stronger than opening stimulation. 



3. Stimulation at cathode on closing, at anode on 

 opening. 



Or, taking the contraction of the muscle as the sign of 

 stimulation, and representing it by C, the law of galvanic 

 stimulation may be expressed thus : — 



1. C.C • CO 



2. CO CO 



3. CCC CAO 



Fig. 23. — To show stimulation at the 

 cathode on closing and at the anode 

 on opening, at the point where the 

 current leaves the nerve. 



Explanation of Elec- 

 tric Stimulation. — A 

 study of the influence 

 of the current while it 

 is flowing throws im- 

 portant light on this 

 point. This condition 

 of the tissue is known 

 as Electrotonus (Prac- 

 tical Physiology). 



While the current simply flows through a nerve no 

 stimulation is produced, but the excitability is profoundly 

 modified. 



Round the cathode the nerve becomes more easily stimu- 

 lated, while round the anode or positive pole it becomes less 

 easily stimulated. This may be expressed by saying that 

 the part of the nerve under the influence of the cathode is 

 in a state of catelectrotouus, of increased excitability, while 

 the part of the nerve under the influence of the anode is in 

 a state of anelectrotomis, of decreased excitability or of more 

 stable equilibrium. This is easily demonstrated by passing 

 a galvanic current along a nerve going to a muscle, and 



