FREDERICK CRESCITELLI 181 



perature and was not the result of some adverse condition in the pro- 

 cedure other than low temperature. This conclusion is suggested by the 

 results of a procedure (fig. 4) performed, not at the low temperature, but 

 at a so-called intermediate temperature. The outcome of this experiment, 

 carried out at 12°C, showed the initial increment but the secondary decline 

 was absent. Exposure to low temperature for a relatively long period was 

 apparently the requirement for eliciting the secondary decrease. 



THE WASH-OUT EFFECT 



In the course of the investigation a finding was encountered which 

 throws some light on the nature of the secondary decline in action potential. 

 This finding, named the wash-out effect, is summarized in its essentials in 

 figure 3. It will be described first of all for the desheathed nerve. At the 

 moment when the A spike had declined to the 80% level, the entire nerve 

 was lifted off the electrode system and immersed in a large volume of 

 Ringer's solution at 2.2°C. The nerve remained in this cold solution for 

 5 minutes (E to F) following which it was quickly replaced on the elec- 

 trodes. Records taken soon after this replacement showed that the A po- 

 tential had been restored nearly completely (fig. 3). Thus a wash-out of 

 the nerve without change in temperature was alone required to reverse 

 the secondary decrease. The wash-out effect was also demonstrable in 

 nerves with intact sheaths but in these cases a much longer period of 

 wash-out was necessary to reverse the secondary block. This point is 

 brought out by the lower graph in figure 3. In this case a 5-minute wash-out 

 in cold Ringer's fluid (A to B) caused relatively little recovery of the action 

 potential whereas a wash-out of 61 minutes (C to D) led to a considerable 

 recovery of activity. These results are explicable in terms of the leak, as a 

 result of cold, of a substance (or substances) which, acting on the nerve 

 membrane, led to the secondary decline. The wash-out procedure, pre- 

 sumably, flushed away the active substance and caused recovery in many 

 of the fibers. The wash-out was less effective in the sheathed preparation 

 because, presumably, the sheath slowed the outward diffusion of the ac- 

 tive substance and made more difficult the procedure of washing it away 

 from the membrane. 



The nature of the active substance (or substances) is unknown but 

 there is good reason to expect that potassium is involved. In conformity 

 with the behavior of other cells, nerves fibers lose extra potassium as the 

 result of low temperature (24, 25). A leak of potassium followed by ac- 

 cumulation at the outer surface might account either entirely or in part 

 for the secondary decline. The wash-out effect is reminiscent of the K-effect 

 of Feng, Hsu and Liu (9). These investigators reported that frog nerves 

 made anoxic by treatment with nitrogen gas would stop conducting but 



