38 ESSENTIALS OF PHYSIOLOGY. 



the nerve which have the same direction as the polarising current. 

 These electrotonic currents are due to ionisation of the electrolytes 

 which occur in solution between the electrode and the axis cylinder. 

 Negatively charged ions are attracted to the anode, with a resulting 

 concentration of ions which are positively charged on the axis cylinder 

 near the anode. In the same way, negatively charged ions accumulate 

 on the axis cylinder close to the kathode. The electrotonic currents 

 are caused by the differences of potential thus produced. 



Electrotonic currents in a nerve can produce the excitatory process 

 in another nerve in contact with the first. If the nerve of a muscle- 

 nerve preparation be laid on a second nerve which is stimulated by 

 single induction shocks, each stimulus sets up electrotonic currents in 

 the stimulated nerve, and these, setting up an excitatory process in the 

 other nerve, lead to contraction of the muscle. 



