178 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



when the blocked nerve segment was treated with solutions all with KCl 

 at five times the Ringer level but with the NaCl varied in the seven steps 

 from 110 mM to 5.5 mM. It is convenient to consider these 'recovery' curves 

 in terms of an initial, rapid restoration, due to sodium, and a phase of 

 secondary block due to potassium. If the initial phase is considered, one 

 sees again the low sodium differentiation between the A and B groups 

 of fibers. Thus a concentration of 11 mM NaCl caused initial recovery 

 in the A but not in the B action potentials. It is evident that the presence 

 of potassium at five times the normal concentration did not alter this 



A— Fl BERS 



B — F IBE RS 



100 



80 



I 60 



H 

 I 



o - 

 X40 



20 



-—66 



i' 1 



-MO 



A' 



\ 



\ 



44 



w 



oLl 



_l_ 



\ 



■ 22 



"T 



T 



I / 

 I / 

 I I 



I I / 



JJi_L?. 



12 



12 



16 P 4 8 



Ml N U T E S 



Fig. 2. 'Recovery' of A and B fibers following block by a solution lacking NaCl. 

 Solutions for 'recovery' all contained 9.0 mM KCl and varying concentrations of 

 NaCl as indicated (in mu) with each individual graph. Tetramethylammonium 

 bromide was employed as the osmotic substitute for the deficient NaCl. 



selective effect of sodium ions. If the secondary phase is considered one 

 sees also the selective behavior in response to high potassium. Thus when 

 secondary block occurred at all it was prominent in the A fibers but absent 

 or small in the B group. These curves also demonstrate that secondary 

 block with a constant level of potassium was, in addition, related to sodium 

 concentration. Thus with a sodium level of 110 mM no secondary block was 

 recorded for the A fibers. As the sodium concentration was decreased below 

 this value the rate of secondary block of the A fibers was markedly en- 

 hanced. This effect may have been the result of an increased rate of 

 depolarization by potassium ions in the presence of a deficiency of sodium. 

 Lundbcrg (19) has reported that certain cations can modify the potassium 



