184 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



nerve still within its moist chamber was then transferred to a second 

 water bath at 21.3°C. After equilibration at this new temperature the 

 potassium treatment was repeated with the results pictured in curve 2. 

 The nerve was then returned to the cold bath at 5.7°C and after equilibra- 

 tion the procedure was once more applied with the result shown in curve 

 3. The final step (curve 4) was a repetition of the procedure at 22°C. Taking 

 into account all the experiments in which the order of carrying out the 

 separate steps was varied (table I), it is clear that progressive changes 

 in the state of the nerve or the previous history of the preparation were 

 not involved in the results. The data demonstrate the occurrence of a sig- 

 nificant increase in the rate of block of the A fibers by means of a solu- 

 tion containing an excess of potassium and acting at low temperatures. 



In view of the possibility of extra loss of intracellular potassium during 

 the experiments at low temperatures, it was desirable to know if, and how 

 much, of the acceleration in rate of block by cold was the result of a po- 

 tassium leak. For this reason an experiment was designed in order to 

 minimize the accumulation of substances around the nerve fibers during 

 exposure to cold. A total of five such experiments was completed and every 

 one led to the same conclusion. The procedure and a typical result are 

 given in figure 6. With the nerve suspended on the electrodes in the moist 

 chamber as for the previous experiment (fig. 5), the blocking action of 

 a solution with KCl at six times the Ringer concentration was first tested 

 at 23.8°C. At this temperature this concentration of KCl led to only a 

 small reduction of the A activity (curve 1). The entire nerve was then 

 placed in a large volume of Ringer's solution at 1.3°C. It was left in this 

 solution for 45 minutes with frequent stirring of the fluid. The nerve was 

 next transferred to a second large volume of physiological solution also 

 at 1.3°C and kept in this for 5 minutes. In this manner the nerve, before 

 recording, was equilibrated at the low temperature in a large volume of 

 frequently stirred solution so as to provide every opportunity for the dilu- 

 tion and removal of substances which might have leaked out of the fibers 

 as a result of the cold. Following this ecjuilibration the nerve was quickly 

 returned to the electrodes; all adjustments were made and in 4 minutes 

 the experiment was begun. The result of the addition of the test solution 

 with KCl at six times the normal level is presented as curve 2. In spite 

 of all the precautions which were taken to prevent the accumulation of 

 active substances, the low temperature still caused a great increase in rate 

 of block. The nerve was next immersed in Ringer's solution at room tem- 

 perature for 65 minutes. It was then set up once more in the moist chamber 

 at 1.3°C and left on the electrodes at this temperature for 54 minutes. 

 Presumably, this ])rocedure would allow for accumulation of substances 

 around the nerve fibers. The action of the test solution was again ex- 



