FREDERICK CRESCITELLI 195 



restoration is indicated by record 38. Immediately after record 38 was 

 taken the choIine-NaCl solution was removed from the nerve segment 

 and was replaced by another solution still with 11 niM NaCl l)ut with TMA 

 in place of the choline. Records 39-41 reveal the outcome of this exchange. 

 The B activity was considerably increased and the conduction delay was 

 decreased. One minute after taking record 41 the choline-NaCl was once 

 again added to the nerve segment with again a reduction in rate of con- 

 duction and in height of B wave (record 42). The bromide ions of TMA 

 were apparently not involved in the TMA effect since no difference in the 

 responses to NaBr and NaCl has ever been observed (records 43 and 44). 

 It appears that the nature of the osmotic substitute was of some signifi- 

 cance in these responses to sodium. This has already been noted (table 2) 

 in connection with the A fibers in which, curiously enough, TMA and 

 choline were found to behave in the reverse manner as in the case of the 

 B fibers. Low temperature was not essential in establishing the point that 

 the osmotic substitute modified the responses to sodium. In a previous 

 study carried out at 23°C (5) it was noted, though no extended study was 

 made of the i^henomenon, that solutions containing 11 mM NaCl in the 

 presence of sucrose were effective in restoring conduction in many B fibers. 

 This did not occur with either choline or TMA. It is not a simple matter 

 to attempt an interpretation of the activity of these so-called inert os- 

 motic substitutes and to account for some of the effects which were ob- 

 served. One thought is that certain organic ions may serve as substitutes, 

 though varying in effectiveness, for sodium ions in the generation of the 

 action potential. Lorente de No (17), in fact, has already postulated that 

 certain quaternary ammonium ions may participate directly in the pro- 

 duction of the nerve impulse and that sodium may actually possess an 

 indirect function. Evidence gathered by the author (5) for the case of 

 tetraethylammonium ions did not support this idea and certainly sucrose 

 cannot be visualized as a substitute for either sodium or ciuaternary am- 

 monium ions. Another interpretation is that these substances so modify 

 the nerve membrane as to facilitate the action of sodium. 



SUMMARY 



It is likely that low temperature produced a multiplicity of effects on 

 the complex system which constitutes the bullfrog nerve trunk. One of 

 these — the leak and accumulation of a substance, probably potassium — 



this is shown in record 38 taken at 106'. At 107' a solution with 11 mM NaCl (but with 

 TMA) was added. Records 39-41 were obtained at 108', 109' and 126'. At 127' a 

 solution with 11 niM XaCl (with choline chloride) was once more applied. The records 

 were followed until no fuither change occurred and the final result is shown as record 

 42 taken at 145'. Recovery is shown first after addition of a solution with 110 mM 

 NaBr (record 43) and finally after Ringer's solution (record 44). 



