78 ANIMAL ELECTRICITY. LECTURE IV. 



e.g., the electrolytic changes within a nerve are modi- 

 fied by irritant and by sedative drugs, and that a 

 poison that kills protoplasm is, from our present 

 standpoint, a reagent that immobilises the living- 

 electrolyte. 



The questions arising in the consideration of the 

 polar reactions of nerve are partly electro-physical, 

 partly physiological, partly electro-physiological, and 

 in this last respect distinctly overlap the narrower 

 province of purely animal electricity. 



Without, then, entering into details such as would 

 be required under the heading of electro-physiology, 

 and considering merely the general features of elec- 

 trical excitation in so far as they involve electrical 

 reactions and their relations to physiological re- 

 actions, these are the main points to be insisted 

 upon. 



It has been laid down by du Bois-Reymond that 

 nerve is excited by a constant current, when that 

 current begins and ends, i.e., at "make " and " break " 

 — but not while it flows, i.e., between the make and 

 break effects. 



It was thereupcMi further proved by Pfluger- — 



(i) That the "make" excitation arises at the 

 kathode. 



(2) That the " break " excitation arises at the 

 anode. 



(3) That during the passage of the constant current 

 excitability is raised at and near the kathode. 



