276 Dr. X. H. Aleock. On the Negative Variation [Jan. 17, 



differences in different animals as regards their reaction to heat, the 

 frog's nerve varies a little according to the condition of the animal, 

 and so the observations have been arranged in two divisions. Here 

 one also notices that the " injury range " is very much smaller than in 

 the warm-blooded nerve, T at most separating a temperature that 

 has no ill effect for one that finally kills the nerve, as against 5 — 6° in 

 the mammal and bird. 



Observations. 



A summary of the previous work on the effect of temperature on 

 nerves is to be found in Howell's* paper, and in that of Boycott 

 (he. eit.). 



Howell, from his own researches, gives 41 — 44° as the temperature 

 at which conductivity is abolished in frog's nerve, the other authors 

 give 45 — 50°. The difference appears to be due to the methods em- 

 ployed. Hitherto, there has been some difficulty in ensuring that all 

 parts of the nerve shall have the same temperature, and this tem- 

 perature has in most cases been ascertained indirectly, further, the 

 time during which the temperature is kept up and the conditions of 

 moisture, &c., greatly influence the results.! 



Another explanation is possible. The majority of observers % have 

 examined the conductivity of nerve as opposed to the excitability, and 

 if the two processes are supposed to be distinct, it might be said that 

 the excitability was extinguished before the conductivity. In view of 

 the considerations stated above, and also of the relation to the coagu- 

 lation point of the proteids, this hypothesis does not seem to be well 

 founded. 



The relationship of the extinction point given above and the coagu- 

 lation point of the proteids in the body of the animal is a very close 

 one. In the frog, the first coagulation of extracted muscle proteid 

 occurs at 40" C,§j| the first step in heat rigor of the muscle itself at 

 38 — 40°, ^ the electrotonic currents are abolished at 40°,** and the 

 extinction point of the neiwes as determined above, 40 — 42° C. 



In the rabbit the proteid coagulation occurs at 47°,§|| the muscle 



* Howell, Budgett and Leonard, " J. Physiol.,' vol. 16, p. 29S. 



f Some earlier experiments I have made under different conditions lend sup- 

 port to these remarks. 



+ Except Edwards' 'J. Hopkins Lab. Studies,' vol. 4, 1887, p. 18(45 — 48° 

 — 55 c ?) ; and Moriggia, ' Moleschott's Untersiichungen,' vol. 14, p. 3S2 (46 — 47°). 



§ Halliburton, loc. ext.; also Halliburton and Mott, ' Archives of Neurology,' 

 vol. 2. 



|| Von Eurth, ' Arch. f. Exper. Path. u. Pharmak.' Leipzig, 1895, vol. 36, 

 p. 231, and ibid., vol. 37, 1896, p. 389. 



r Tincent and Lewis, ' J. Physiol.,' vol. 36, p. 445 ; see also Brodie and 

 Richardson, 'J. Physiol.,' vol. 21, 1897, p. 353, and ' Phil. Trans.,' B, vol. 191, 

 1399, p. 127; and also Yernon, c J. Physiol.,' vol. 24, p. 239. 



** Waller, £ Eoy. Soc. Proc.,' vol. 60, p. 384. 



