POLAR EXCITATION OF NERVE. 



5°3 



occurs in a nerve, the total functional capacity of which has fallen through the 

 experimental procedure ; such a fall, particularly in the intrapolar region, is 

 produced in consequence of the passage of currents of considerable intensity, 

 and is manifested by delayed transmission lasting for some little time after the 

 current has ceased. Localised changes of a less pronounced type, at the anode 

 on closure and at the cathode on opening, undoubtedly cause slight retardation, 

 and account for those cases where the extra delay is small. 



Duration of Periods of Delay in Muscle Response to Excitation 

 of its Nerve by Galvanic Current. 1 



Polak Excitation of Nerve by Electrical Currents. 



Pfhiger's law of contraction.— The passage of a galvanic current 

 through a motor nerve of sufficient duration to allow the muscular re- 

 sponse evoked at closure to be distinct from that at opening, causes effects 

 which vary in accordance with the intensity and direction of the current ; 

 they may be tabulated as regards their production into stages as follows: — 



The muscular effects produced in the first two stages are dependent 

 upon the circumstance that, at closure, the nerve excitation takes place 

 at the cathode, and is associated with the sudden development of the 

 state of lessened molecular stability ; at the moment of cessation it 

 takes place at the anode, and is associated with the sudden rebound 



1 The delay in the response to nerve excitation by the closing or opening of the galvanic 

 current is in each case compared with that present when the nerve is excited by an induced 

 current. 



