186 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



In attempting to interpret the action of cold in accelerating the potas- 

 sium block the first thought which comes to mind is that low temperature 

 enhanced the rate of depolarization by potassium ions. There is, in fact, 

 some support for this interpretation. In a previous publication (7) the 

 author pointed out the observation that the rate of depolarization by a 

 solution containing 11 niM KCl was greater at 5.2°C than at 23.6°C. 

 Lundbcrg (20), too, presented some evidence that low concentrations of 

 potassium, such as those of the present investigation, caused a depolariza- 

 tion which was initially faster at 7°C than at 20°C. Curiously enough, 

 this action of cold was found when the nerve was in an atmosphere of 

 oxygen but not in an atmosphere of 95% Oo and 5% CO2 . With higher 

 concentrations of potassium Lundberg was unable to find any influence 

 of temperature on the rate of depolarization. In addition there is the 

 statement by Feng and Liu (8) "that as a first approximation the rate of 

 potassium depolarization in nerve may be regarded as practically inde- 

 pendent of temperature". The status of this question is therefore still 

 somewhat uncertain and must await the elucidation of more of the factors 

 which are involved. There appears to be enough evidence, however, to 

 warrant the tentative conclusion that acceleration of potassium block by 

 cold is directly related to the depolarizing action of potassium. This con- 

 clusion does not rule out, of course, the possibility that other factors may 

 be involved; for example, that the level of depolarization which is re- 

 cjuired to produce block varies with temperature. It is interesting to note 

 at this point that depolarizations l)y different substances are influenced 

 quite differently by cold. In addition to the types of actions already 

 mentioned for potassium there are well authenticated examples of inhibi- 

 tion of depolarization by a reduction in temperature. The author (7) pro- 

 vided an example of this in the case of amyl carbamate which, in certain 

 concentrations, caused a progressive depolarization, an effect which was 

 effectively abolished by cold. The depolarization associated with veratrine 

 was found to be similarly inhibited by cold (20). The ions of ammonium 

 and lithium ai^parently differ from that of ]iotassium in that their de- 

 i:)olarizations are delayed by low temperature (20). The nerve membrane 

 potential can apparently be reduced by a number of actions. 



RESPONSES TO POTASSIUM B FIBERS 



It has already been pointed out that the A group of fibers is more readily 

 blocked by solutions with excess potassium than is the group of B fibers. 

 This fact was noted by Lorente de No (15) for the bullfrog sciatic nerve. 

 Differential block by excess potassium was also noted in difl'crent groups 

 of mammalian nerve fibers bv Lundberg (21 ). The diff'erential sensitivity 



