1903.] Phenomena in Mammalian Non-meclullated Nerve. 175 



Experiments 721 and 720 were with non-medullated and medullated 

 nerves under the same conditions. 



Considering the result of all these experiments, it is clear that the 

 diminution of the negative variation in non-medullated nerves is 

 due to changes occurring at the point where the nerve is excited. 

 Using a constant stimulus this spot becomes less and less excitable, in 

 the sense that the response becomes progressively smaller. The 

 control experiments on medullated nerve show but slight traces of 

 this effect,* either the medullary sheath prevents this loss of excita- 

 bility in some way, or the two classes of nerves differ very widely in 

 their reaction to stimuli. Speaking broadly, the evidence is in favour 

 of the former hypothesis. 



While the work of Sowtonf and GartenJ on cold-blooded nerves 

 is in accord with my results on mammalian nerve, the paper of Brodie 

 and Halliburton at first sight offers a contradiction. These experi- 

 menters excited the splenic nerves in the dog for many hours, and 

 blocking the impulse by cold, observed that when the block was 

 removed the splenic contractions followed as at first, apparently un- 

 altered in amount. I have no doubt as to the correctness of their 

 observations, and the results they obtained, differing from those 



Fig. 7.— Splenic of Horse. Effect of Ether Yapour. 



* Dr. Waller has very kindly permitted me to measure a considerable number of 

 his photographic records of frog's nerve, of 1896 — 1897 ; in all a small regular 

 diminution is detectable, amounting to from 2*0 to 5"6 per cent., in experiments 

 lasting 40 minutes. 



f Sowton, loc. cit. 



1 G-arten. 



