INFLUENCE OF TEMPERATURE. 



555 



diminution when the nerve was stimulated. Boruttau thus concludes 

 that these non-medullated nerves show electrotonic changes of precisely 

 the same character as those present in medullated nerves, and that such 

 difference as exists is merely a quantitative one, due to the diminished 

 susceptibility to electrolytic polarisation, consequent upon the small 

 extent of the nerve sheath. 



Influence of temperature. The sciatic nerves of large cooled 

 frogs, if kept at a low temperature during the experiments, show- 

 results which Biedermann considers to be analogous to those of the 

 Anodon non-medullated nerve. If the galvanometer electrodes are 

 connected at a distance of 3 cms. from the polarising, and contacts 

 made with the portion of cooled nerve left in its natural connection 

 with the gastrocnemius muscle, then the resting difference and 

 excitatory electrical response are both so small as not to affect 

 the galvanometer. Under these circumstances an anelectrotonic 

 extrapolar effect is noticed, whilst the catelectrotonic effect is very 

 small. In one of Biedermann's experiments, the former amounted to 

 6, the latter being absent. 1 On now approaching the galvanometric 

 contacts to 17 mm. from the polarising ones, the anodic effect 

 was 20, the cathodic 2. At 11 mm. the anodic was 34, the cathodic 

 13. The nerves of the cooled frog are thus in a state which accentuates 

 the normal discrepancy between the amounts of the anodic and 

 cathodic electrotonic effects. This accentuation is regarded by Bieder- 

 mann as due to increased susceptibility of the nerve to the physiological 

 reaction at the anode. It appears, however, that the influence of 

 temperature is a complicated one. Waller has observed that both 

 electrotonic currents fail when the temperature of the whole sciatic 

 nerve is raised to 40 C. or lowered to C., returning when the 

 temperature is brought back to 15 C. 2 He observed, also, that after 

 prolonged exposure to these temperatures, electrotonic effects are not 

 produced at ordinary temperatures, whilst after a moderate exposure 

 to 40 C. the effects at 15 C. are perceptibly altered, the cathodic 

 being increased and the anodic diminished so much that the latter may 

 become less than the former. 



It is therefore doubtful how far the experimental data brought forward 

 by Biedermann justify the arbitrary division of electrotonic phenomena 

 into two classes. The particular terms employed to describe these 

 two classes, " physical " and " physiological," the present writer is 

 unable to accept. Such a distinction in no way facilitates the physio- 

 logical conception of the changes in a living nerve. For it is clear 

 that the physiological changes which Biedermann desires to accentuate 

 must have a physical basis as their causative factor. As Boruttau has 

 most pertinently remarked, some physical change must be assumed even 

 by those who take Biedermann's view, and this is presumed to be some 

 chemical rearrangement of a synthetic type at the anode, which is obvi- 

 ously produced by the passage of the current. 3 The only known chemical 

 rearrangement at the anode is electrolytic in character. Whether, 

 therefore, electrotonic phenomena have an electro-chemical basis only, 

 or involve, as Biedermann insists, an electro-chemical basis, plus a further 

 "unknown" chemical change, the releasing causative factor is physical, and 



1 Biedermaim, ' ' Elektrophysiologie, " S. 691. 



2 Waller, "Proc. Physiol. Soc.," Journ. Physiol., Cambridge and London, vol. xx. 



3 Boruttau, Arch. f. d. ges. Physiol. , Bonn/1896, Bd. Ixiii. S. 145, 158. 



