196 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



was very likely the cause of the secondary decrease in action potential 

 (fig. 3). Such a leak and accumulation possibly contributed a component 

 to some of the other low temperature actions which were observed. The 

 excess potassium block at low temperature (fig. 6) probably received a 

 contribution from this source. For this investigation the exjieriments in- 

 volved an attempt to minimize the accumulation of potassium by treating 

 the nerve segment with several changes of test solution and by making 

 each experimental run as short as possible. The nature of the evidence, 

 already discussed in the body of this paper, leads to the thought that 

 additional actions of cold, possibly direct effects on temperature sensi- 

 tive systems, were also involved in some of the results. This statement 

 has support from some data in the published literature. The initial increase 

 in action potential with time (figs. 3 and 4) as the nerve cooled can be 

 accounted for, at least in part, by the fact that the spike heights and spike 

 areas of individual nerve fibers increase as the temperature is lowered. 

 This fact is clearly brought out by the investigations of Schoepfle and 

 Erlanger (22) and of Hodgkin and Katz (13). Both groups of investigators 

 noted an augmentation in spike height of single fibers and a large in- 

 crease in spike area as the result of lowering the temperature. The falling 

 phase of the spike was found to be slowed more than the rising phase. 

 Hodgkin and Katz reported Qio values between 10 and 20°C to be 2.0 

 for the ascending phase and 3.2 for the falling period. Tasaki and Fujita 

 (26) employed single fibers from the toad and obtained results which were 

 in general agreement with the above data as far as the spike area was con- 

 cerned. They reported an increase in duration of spike in passing from 

 20° to 5°C, the Qio of the process being 3.5. With regard to spike height 

 these workers observed, not an increase, but a small though continuous 

 decline in cooling to 5°C. Another report on the effects of temperature on 

 single spike activity is that of Hertz (11) who found for frog nerve fibers 

 little change in spike height down to about 10°C. Below this value the 

 height decreased slowly. A few investigators have employed nerve trunks 

 for studies of the effects of temperature. Gasser's well-known study utiliz- 

 ing the sciatic nerve of the frog presented evidence of a notable decrease in 

 compound spike below about 20°C (10). Lorente de No (15) employed 

 the bullfrog sciatic nerve and noted an optimum temperature range for 

 A-alpha fibers at 10°-15°C. There is, as indicated by this brief summary, 

 some disagreement in the literature with regard to the details of the re- 

 sponses to temperature. This is not surprising since many factors probably 

 determine the exact manner in which temperature will influence the height 

 of the spike in a given preparation. Changes in resistance, ion shifts, length 

 of exposure to low temperatures (figs. 3 and 4) and other factors are all 

 involved. When comparing different types of nerve fibers or nerve fibers 



