FREDERICK CRESCITELLI 197 



from different animals additional factors come into play. Lundberg (18), 

 for example, published records which demonstrated notable differences in 

 temperature optima for mammalian A and C fibers. The phenomenon of 

 temperature adaptation (2-4), unless recognized, could offer in different 

 nerves from the same animal or the same nerve from different animals a 

 source of troublesome variability. In spite of differences in the literature, 

 the conclusion is clear that temperature-sensitive processes do exist in the 

 sequence of events leading to spike formation. 



Such processes are probably at the basis of the finding that cold selec- 

 tively influences the sodium requirements for spike production in the A 

 and B fibers of the bullfrog sciatic nerve preparation. The interpretation 

 which was offered this phenomenon is that for both A and B groups of fibers 

 there are processes with optimum temperatures — characteristically dif- 

 ferent for the two fiber groups — for the action of sodium in generating a 

 spike. This idea is speculative and based only on the sodium responses of 

 the A and B fibers at normal temperature and at low temperature. It 

 should be possible in the future to test this idea by working out in an ap- 

 proximate manner the form and location of the temperature-sodium re- 

 sponse curves for both A and B fibers. In the meantime there are the results 

 of Lundberg (18) which suggest the same idea for mammalian A and C 

 fibers. Lundberg recognized a number of objections to his procedures; 

 namely, the use of different species of animals, the use of different nerves 

 as a source of different fibers types leading, of necessity, to differential 

 treatments of the various fiber types. These objections disappear in the 

 present experiments since one was dealing here with different fibers in the 

 same nerve and tested at the same time. 



The notion of processes in nerve fibers with different characteristic 

 temperature curves is of more than passing interest. Such systems are the 

 sort of thing that one might expect to find in temperature receptors, for 

 example. Such a motive is undoubtedly behind investigations such as that 

 of Bernhard and Granit (1) who utilized peripheral nerve as a 'model 

 temperature end organ'. The existence of characteristic temperature-sen- 

 sitive systems in nerve cells is also of interest to the environmentalist who 

 wishes to know if, and to what extent, environmental temperature changes 

 can influence such systems and whether or not such effects are permanent 

 in the organism. This aspect of temperatures analysis in biology has re- 

 cently received an impetus from the studies of Chatfield and his group 

 (2-4). They reported (2) that the tibial nerves from an hibernating mam- 

 mal (the golden hamster) were able to conduct down to a temperature of 

 3.4°C whereas the comparable nerves from the non-hibernating albino 

 rat ceased activity at 9.0°C. The curves relating action potential height 

 with temperature were different for the two species. In another study (3) 



