1903.] 



in the Nerves of Warm-blooded Animals. 



273 



■observed in the bird (Experiment B") and not in the mammal. In 

 the case of CO-j this increase is seen in all the warm-blooded nerves ; 

 primary and secondary augmentation are shown in Exp. B m from 

 the pigeon, and the latter, in fig. 4, from the rabbit. 



I do not here enter upon any discussion of the actual mechanism of 

 this increase, it may be due to either of two causes — increase of 

 E.M.F. or increased duration of electromotive change. The latter 

 explanation has been suggested by Gotch as being the true one. 



The effect of tetanisation (fig. 5) has not been marked. Three 

 experiments proved negative, and two gave a slight increase, so that 

 this question is still undecided. 



It appears, therefore, certain that neither in the voltage of the 

 negative variation, in the strength of excitation, or in the action of 

 anaesthetics is there any marked difference between the warm-blooded 

 and amphibian nerves, and that all the facts ascertained for the latter 

 under these heads can be applied en bloc to the former. 



Temperature of Extinction by Heat. 



Three series of experiments on frogs, mammals, and birds were 

 undertaken to ascertain the precise point at which the negative varia- 

 tion was abolished by heat. 



Method. — The nerve chamber was kept at a constant temperature 

 throughout, e.g., 30° C. The nerve itself was placed on the electrodes, 

 and when it had reached the temperature of the chamber, the value of 

 0*001 volt was determined on the galvanometer scale, and then the 

 values of the first six negative variations. The nerve was then 

 removed, placed in 1*05 per cent. NaCI solution (containing Ca 

 salts, &e.) at the desired high temperature (e.g., 49° C), left for exactly 

 5 minutes, placed in cool (18° C.) salt solution for 7 minutes. A 

 fresh transverse section was made, the nerve was replaced on the 

 electrodes, and the value of 0*001 volt and the second set of six nega- 

 tive variations determined. 



This method fulfils several desiderata. 



(1.) It is possible to keep the beaker of hot saline solution at any 

 given temperature with an error of less than ± 0*1° C. 



A standardised thermometer was placed in the bath close to the 

 nerve, and with 5 minutes immersion all parts of the nerve reach the 

 temperature of the solution. 



(2.) Any alteration in the resistance of the nerve is readily detected 

 by means of the standard deflection with 0*001 volt, and as both 

 readings are taken at the same temperature, this alteration must be a 

 permanent one, and not the temporary alteration always seen when a 

 nerve is heated or cooled. 



(3.) Using a concentration of salt solution* that had been found to 



* No carbohydrate was added to the solution in any of the heat experiments. 

 The solution was neutral. 



VOL. LXXI. X 



