CHAPTER VIII. 



1 Electrotonus ; 2, Modifications of excitability : 3. Law of pulsa- 

 tions ; 4. Connection of electrotonus with excitability; 5. Trans- 

 mission of excitability in electrotonus; 6. Explanation of the 

 law of pulsations ; 7. General law of nerve-excitement. 



1. It has already been observed that a constant elec- 

 tric current, if transmitted through the nerve, is able 

 to excite the latter; but that this exciting influence 

 takes effect especially at the moment at which the cur- 

 rent is closed and opened, and that it is less effective 

 during the course of the current's duration. As yet it 

 has been desirable for our purpose, that of studying the 

 process of excitement in nerves, to make use of induc- 

 tive currents, which are of such short duration that the 

 closing and the opening, the beginning and the end, 

 immediately follow each other in quick succession. 

 Without now entering into the question, to be dis- 

 cussed later, as to why the exciting action of the cur- 

 rent is less during the steady flow of the latter than at 

 the moments of closing and opening, we will now ex- 

 amine whether the electric currents which traverse the 

 nerves do not act on the nerves in some other way, 

 distinct from their exciting influence. 



Let us suppose that the current traverses either the 

 whole or a portion of a nerve. At the instant at which 

 the current in the nerve is closed, the appropriate muscle 



