FREDERICK CRESCITELLI 



189 



(5) that activity could be restored in a majority of A fibers whereas solu- 

 tions with slightly lower concentrations of NaCl caused either no recovery 

 or only slight recovery. With such a limiting concentration of sodium ions 

 it w^as observed that low temperature markedly retarded recovery of 

 blocked A fibers. An example of almost complete inhibition is furnished 

 by the data in curves 2 and 4 in figure 8. At normal temperature the solu- 

 tion with 11 niM NaCl yielded restoration of A activity to well over the 



100 



80 



(-60 



X 



o 



I 



"40 



20 



"1 1 1 1 



\ ^^ 



"T 1 1 r 



« ^lOVCj 



■ 22*C 





, 22 7t \ \ * \ 



II XX 



/? 



i^"' 



J 

 'i 



— .-I 



' I 



I 



I I 

 I I 



a 



on xxt 



J L 



J L 





I I 

 I I 



-_ __ o o o_ 



I I 



4 8 ""12"TES ,^ ^^ ^^ ^^ 



Fig. 8. Conduction block and recovery of A fibers at normal and at low temperatures. 

 The four steps were carried out consecutively as numbered using the same nerve 

 preparation. At zero time a solution without NaCl but with TMA as the substitute 

 was added. At points indicated as .011 the test solution with NaCl at the limiting 

 concentration was added. Ringer wash occurred at R. Temperatures are indicated by 

 lines connected to each graph. 



60% level (curves 1 and 3). At low temperature (curves 2 and 4) this test 

 solution caused practically no restoration of action although Ringer's 

 solution was perfectly effective. There is also evidence that the responses 

 to sodium were also influenced by the nature of the osmotic substitute. 

 As the data in table 2 suggest, recovery of the A fibers was less when TMA 

 was employed than with choline. The retarding effect of cold on the re- 

 covery responses to sodium is interesting for it suggests the existence of 

 a temi)erature-dependcnt system in tiie active membrane. Since the sodivmi 

 conductance through the membrane depends on the membrane potential 

 (14) it might be that cold exerts its effect by acting directly on this po- 



