180 Electromotive Phenomena in Non-medullated Nerve. 



As the electrotonic currents are so small, it was not to be expected 

 that there should be any marked alteration of excitability in the 

 neighbourhood of the kathode or anode of a constant current. 

 Three experiments were, however, made to serve as a check on the 

 preceding : — 



Table VIII. 



Experiment. 



Xeg. var. 

 (mean) . 

 Initial. 



Xeg. var. 

 (mean), 

 during 

 anelec. 



Xeg. var. 

 (mean) 

 during 

 katelec. 



Xeg. var. 

 (mean). 

 Final. 



Xotes. 



743, X. Polarising cur- 

 rent = 0"5 volt. 

 Excitation = 1000. 



-488 



-468 



0-452 



0-460 





744, X. Polarising cur- 

 rent = 2 volts. 



0-492 



0*453 



-444 



0-434 



Same nerve 

 as 743. 



745, X. Polarising cur- 

 rent = 2 volts. 



-971 



0-931 



0-928 



0-8S4 





The exciting electrodes were at a distance of 3 mm. from the 

 polarising, and on their distal side. From an inspection of the figures 

 it is clear that even taking the most favourable case of the last 

 <experinient the effect is a minimal one. 



I have much pleasure in acknowledging the kind assistance and 

 advice I have received from Dr. Waller in the prosecution of this 

 research, and also in expressing my indebtedness to the Council of the 

 -Zoological Society and Dr. Chalmers Mitchell for permission to use 

 the nerves of the horses which had been slaughtered for the carnivora. 



Conclusions. 



1. ^Non-medullated nerves exhibit a negative variation and current 

 •of injury of about three times the magnitude of the similar phenomena 

 in the medullated nerves of the same animal. 



2. The negative variation of non-medullated nerves undergoes a 

 progressive diminution with repeated stimuli. 



3. The immediate cause of this diminution is a localised change at 

 the place of excitation. 



4. The electrotonic currents of non-medullated nerves are very small, 

 about one-fortieth of those in medullated nerves. 



5. This latter fact affords an explanation of 2 and 3, as the exciting- 

 current, being confined to the place of application, has a greater current 

 density and therefore a greater local effect. 



