FREDERICK CRESCITELLI 



191 



little uptake of sodium should be expected and possibly a loss of this 

 cation actually occurred. 



RESPONSES TO SODIUM-B FIBERS 



Perhaps the most unexpected action of low temperature was in regard 

 to the behavior of the B group of nerve fibers. As already indicated the 

 B fibers at normal temperatures were more rapidly blocked by solutions 

 lacking NaCl and required, for recovery, a higher concentration of sodium 



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'M I N U TT S 



Fig. 9. Selective block and recovery of A and B fibers at 23.5° and 3.2°C. At zero 

 time a solution without NaCl was added, using TMA as the osmotic substitute. At 

 points indicated by .011 a solution with the limiting concentration of NaCl was 

 applied. Ringer wash took place at R. 



ions. Low temperature produced a significant modification in tlie reactions 

 of the B fibers to sodium. One aspect of this modification is shown in 

 records 22-44 of figure 7. These electrograms illustrate the point that at 

 normal temperature the B fibers blocked significantly ahead of the A 

 fibers (records 35-39). At the low temperature, on the other hand, the two 

 groups blocked almost simultaneously (records 22-31 ). In other words cold 

 led to a breakdown of the differential action of the low sodium solution. 

 The graphs in figure 9 reveal another aspect of this modification. At 23.5°C 

 (curves 2A, 2B) a typical low sodium cessation of action was observed 

 with the B fibers (curve 2B) blocked well ahead of the A fibers (curve 

 2A). At the 8 minute point a solution with the limiting concentration of 



