ICHIJI TA.SAKI AND COXSTANTINE S. SPYROPOULOS 209 



bomb) was of the 'outside-cap compression closure' type. The inside di- 

 ameter of the vessel measured S^Xe in. and the depth of the vessel 10 in. 

 Six self-sealing electric connectors were installed in the inner pressure head. 

 The pump, reaction vessel and the connecting i/4-in. superpressure tubing 

 were filled with mineral oil. The glass vessel containing a single fiber prep- 

 aration in a volume of Ringer (or sea water in case of a squid axon) was 

 immersed in the mineral oil in the pressure bomb. 



The coefficient of compressibility and the specific heat of the mineral 

 oil are such that with an increase in pressure of 15,000 psi the temperature 

 of the oil may increase by as much as 10 degrees. The rise in temperature 

 of sea water or Ringer was (for the same increase in pressure) less than 

 %th the rise of mineral oil. In order to minimize the effect of a change in 

 temperature due to compression, it was necessary to avoid immersing the 

 nerve fiber directly in mineral oil. Equilibration at the desired temperature 

 was achieved by the flow of water, from a regulated temperature bath, 

 through a coil of super-pressure tubing surrounding the nerve preparation. 



EFFECTS OF TEMPERATURE CHANGES ON NERVE FIBER 



Resting Potential. The effect of temperature changes upon the resting 

 membrane potential of the isolated myelinated nerve fiber has not yet 

 been investigated. On the squid giant axon, Hodgkin and Katz (12) have 

 shown that the resting potential is practically independent of the tempera- 

 ture in the range between and 20°C. The resting potential of the skeletal 

 and cardiac muscle has also been found to be only slightly affected by 

 temperature changes (22-24). 



Membrane Capacity and Resistance. The capacity of both the myelin 

 sheath and the nodal membrane has been found to be practically inde- 

 pendent of temperature in the range between 14° and 25°C (17). Similarly 

 the capacity of the squid axon membrane did not show any appreciable 

 temperature dependence between 3° and 23°C. 



The membrane resistance, on the contrary, showed an appreciable tem- 

 perature dependence in the frog myelinated fiber (17). The resistance of 

 both the myelin sheath and the nodal membrane (in choline) increased by 

 50 to 80% when the temperature was lowered from 25° to 15°C. An equally 

 strong temperature dependence of the membrane resistance has been ob- 

 served by Tamasige (25) in the muscle fiber of the frog. Del Castillo and 

 Machne (26) however using a different method reported a slightly lower 

 Qio (1.35) for the muscle fiber membrane. Coraboeuf and Weidmann (23) 

 found a Qio of 1.49 for the membrane resistance of Purkinje fibers. In the 

 squid giant axon the membrane resistance at rest was not appreciably 

 affected by temperature changes. In the range between 5° and 25°C, the in- 

 crease in the resistance for a fall of 10° was about 9-25%. Since the squid 



