POLARIS A TION AND EXCITA TION. 5 5 7 



excitation ; this prolonged opening response, evoked at the anode, 

 causes anodic negativity such as must occur in consequence of any pro- 

 longed excitation. Such an excitation can undoubtedly occur in a 

 muscle, where it is evidenced by an initial propagated twitch and a 

 prolonged localised contraction, the latter being produced on opening 

 intense currents. Both of these opening contractions fail if the anodic 

 tissue is injured. 



In nerve, no evidence of a similar prolonged localised excitation 

 at the anode, when a current is opened, had up to the discovery 

 of the phenomena now referred to, been found. Opening tetanus 

 is a proof that a series of propagated excitatory states may be 

 produced, but a localised change without propagation can only be 

 indicated by a localised electrical effect. If the anodic opening after 

 effect is such an indication, the phenomena of nerve excitation are 

 brought into strict accord with those of muscle. In both tissues the 

 excitatory anodic after effect fails, or is markedly diminished if the 

 anodic contact is upon a thermal section, 1 and is decreased in amount 

 if the tissue is in a state of excitation. 2 



A point raised by the presence of this anodic change has reference 

 to the causation of such opening contractions as are obtained in the 

 second stage of Pfluger's law of contraction. 



The discovery of the opening excitatory effect at the anode, renders 

 it difficult to accept the theory advanced by Griitzner and by Tiger- 

 stedt as to the causation of opening excitation. 3 According to this 

 theory, the polarisation current, which comes into full play when a 

 current is opened, is the presumed cause of the anodic excitation, for 

 this is now the cathode of the polarisation counter after effect ; hence 

 all excitation is on this view reduced to the production of cathodic 

 changes. It is evident that a prolonged excitation on breaking a 

 current intense enough to cause an anodic excitatory after effect cannot 

 be due to such counter polarisation current, since this is itself over- 

 powered and replaced by an electrical change of opposed sign. Under 

 these circumstances, the anode does not become the cathode of a 

 counter current. 



Polarisation and excitation. It follows from the whole of the 

 facts previously detailed, that the connection between the electro- 

 lytic action of a current and its exciting efficiency is, in the case 

 of nerve, a very intimate one. Indeed, the two appear to be so 

 blended that the determination of the conditions which influence 

 polarisation, as well as the character of the polarisation changes, appear 

 to many to constitute the surest road by which the physiologist 

 may reach his goal and acquire more exact conceptions of the excitatory 

 state. 



It is therefore a matter of great interest to consider, in conclusion, 

 how far the phenomena of nerve justify the conclusion that the 

 relationship between the electrolytic action and the exciting efficiency 

 of electrical currents is -so indissoluble, that the possession of the 

 latter involves, as a necessity, the production of the former, and vice 

 versa. 



In the first place, what evidence is there that an exciting current 



1 Hermann, Arch. f. d. ges. Physiol., Bonn, Bd. xxxiii. S. 103. 



2 Stewart, Journ. Physiol., Cambridge and London, 1888, vol. ix. pp. 26 and 199. 



3 Grutzner, Arch. f. d. ges. Physiol., Bonn, 1883, Bd. xxxii. S. 357. 



