210 INFLUENCE OF TEMPERATURE ON BIOJ.OGICAL SYSTEMS 



axon membrane resistance is not independent of current (18), there is 

 some arbitrariness in this measurement. 



This relatively significant difference in the temperature dependence of 

 the resting membrane resistance between the frog nerve fiber and the 

 squid axon could be ascribed to the existence of many cut branches in the 

 latter fiber. It is our impression that there were in the area of 1 cm- of the 

 giant axon membrane (i.e. in the region of 6-7 cm length) usually 10-30 

 cut branches. The diameter of these branches was often larger than 50 fx. 

 If the regions of the membrane where the branches were cut were to be 

 considered as holes devoid of any highly resistive cap, then the sum of the 

 electric conductance of these holes cannot be far smaller than the con- 

 ductance through the intact portion of the membrane. If this be the case 

 we have studied the low temperature dependence of the shunting holes 

 rather than that of the 'membrane' proper. 



Resistance of the Axoplasm. There is at present no accurate measure- 

 ment of the temperature dependence of the axoplasmic resistance on the 

 frog myelinated nerve fiber. Hodler, Stampfli and Tasaki (27) have shown 

 that sudden cooling of a part of an internodal segment caused a decrease in 

 the size of the action current recorded across the same internode. From 

 these experiments it seems very likely that the axoplasmic resistance in- 

 creased with a fall in temperature. A strong temperature dependence (Qio of 

 about 2) of the resistance of the sarcoplasm of the frog muscle fiber was 

 reported by Tamashige (25). Coraboeuf and Weidmann (23) reported a 

 Qio of 1.48 for the myoplasmic resistance of the Purkinje fibers. In the 

 squid giant axon, a recent measurement by Schmitt (28) showed that the 

 axoplasmic resistance increases by about 30% for a fall in temperature of 

 10° (between 5° and 25°C). 



Action Potential. In the range of temperature between 5° and 25°C, 

 the spike amplitude of the action potential of the myelinated nerve fiber 

 of the toad was found to be 100-110 mv (10, 16). In the squid giant axon, 

 Hodgkin and Katz (12) showed that the spike amplitude increases very 

 slightly (5-10%) with a drop in temperature from 20° to 2°C. Similarly 

 in the cardiac muscle the spike amplitude of the action potential was found 

 to be independent of temperature (23, 24). 



The spike duration of the action potential, on the contrary, was found to 

 increase significantly with a fall in temperature. In the toad motor nerve 

 fiber (8) , the value of the Qio was about 3.5 (see curve d in fig. 4) . In the 

 squid giant axon, a Qio of 3-3.5 has been reported for the falling phase of 

 the spike potential (12). The rising phase of the action potential is known 

 to show a smaller temperature dependence than the falling phase ; in the 

 squid axon, it has been reported that the Qio is close to 2 (12). In the 

 frog nerve fiber, however, the shape of the rising phase was determined 



