FREDERICK CRESCITELLI 



185 



amined with the outcome shown in curve 3. The rate of block was greater 

 in this third section than in the second section of the series leading to 

 the thought that substances which leak out and accumulate may con- 

 tribute a component to the result. The fourth and fifth sections were 

 carried out in order to remove the possibility of an effect due to pro- 

 gressive changes in the condition of the preparation. Following the third 

 section, just described, the nerve was placed directly into Ringer's fluid 



100 



80 



— r-o o— , 



60 



I 

 I 

 <40 



20 



lip 

 11' 



".^ 

 i' \ 





-o— ^ 2^3 8"C 



-o-J 



1 

 I 



— r 

 I 





; 1 





\ 



/ 



0/ 



'/■ 



\l 3*C 





MS'C' 



A 







II 



I I 



:r-o — -, 





4 8 12 16 20 24 



MINUTES 



Fig. 6. Conduction block of A fibers produced by excess potassium, i.e. 10.8 m.M KCl. 

 Curve 1: block and recovery at 23.8°C; nerve on electrodes in air. Curve 2: block 

 and recovery at 1.3°C after period of equilibration in cold Ringer's solution. Curve 

 3: block and recovery at 1.3°C; nerve on electrodes in air. Curve 4: block and recovery 

 at 1.3°C with preliminary wash-out. Curve 5: block and recovery at 24.2°C; nerve 

 on electrodes in air. 



at 1.3°C and left there for 15 minutes during which time the fluid was 

 frequently agitated. After this washing the nerve was returned to the 

 electrodes and the potassium block was once more recorded (curve 4). 

 The result reinforces the suspicion that, though the accumulation of an 

 active substance made a contribution to the block, there was in addition 

 a main effect of temperature itself on the nerve fiber which resulted in 

 an acceleration of block by potassium ions. The fifth and final segment 

 of the series (curve 5) simply illustrates the point that the normal tem- 

 perature response was still obtainable from a nerve jireparation which 

 had suffered a rather rigorous series of low temperature treatments. 



