280 Dr. K H. Aleock, On the Negative Variation [Jan. 17 



using the same apparatus that Waller* employed in his researches of 

 the effect of temperature on the electrotonic current of frog's nerve. 



The negative variation was observed in the way before mentioned. 

 The value of the galvanometer deflection was ascertained by taking 

 the scale value of 1 millivolt at intervals. It was found, as is well 

 known, that the resistance of the nerve and electrodes gradually 

 increased as the temperature was lowered, and this causes a small 

 error in the strength of excitation, though this was annulled as 

 far as possible by an added resistance of 100,000 ohms in the exciting 

 circuit. 



Comments. 



The limits determined are for the temporary abolition of the 

 negative variation, not for its permanent abolition. There is a 

 gradual rise of the extinction point through the four classes of amphi- 

 bians, hibernating mammals, mammals and birds. The limit varies a 

 little in each experiment in a manner that is not accounted for by 

 either the apparent condition of the nerve or by its anatomical character, 

 That some variation was to be expected was clear from the researches 

 of Howell,f who found that the vaso-constrietor fibres in the cat's 

 sciatic were paralysed by cold ( + 4° C. q.p.), while the vasodilatator 

 fibres were paralysed 1 lower, and even greater differences were 

 observed between the cardiac and respiratory fibres in the vagus. 



Taking the experiments as they stand, it is evident that those upon 

 which most reliance can be placed, are where the nerve has reached 



MilUvoLbs. 















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VN 





















Jj 

















































- 



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^ 



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— ! 



5° J4° /3° 12? l!° 10° 9° i 



3° 7° 6° 5° 4° 3° 2.° 1° 0° - 



<°-2 



Degrees CenCigns.de. 



Fig. 7. — Exp. C df . Yalue of the negative variation in nerve of hedgehog at 

 different temperatures. 



* Waller, ' Proe. Physiol. Soc.' in 1 J. Physiol.,' vol. 20. 

 + Howell, loc. ct't. 



