114 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



Fig. 24. — Action potentials of the tibial nerve of a hamster (on left) and of a rat (on right) 

 at various temperatures. The action potentials of the hamster were all recorded at the same 

 gain. The three potentials of the rat lowest in the figure were taken at a higher gain than had 

 been previously used in this experiment. Note that even with high gain the action potential in 

 the rat has disappeared at 10° C. while even with less gain the potential of the hamster is still 

 perceptible at 2.5° C. 



in this case, for the same results were obtained from the nerves of hibernating and 

 nonhibernating hamsters. This resistance to cold appears to be a peculiarity of the 

 peripheral nerves of all animals that hibernate, for similar results have been obtained 

 in the woodchuck.^-^ As was shown above (see Metabolisiii, page 91 ), the hibernat- 

 ing animal reacts with increased metabolism to environmental temperatures below 

 3° C. This is approximately the temperature below which the peripheral nerves will 

 cease to function. 



THEORIES OF HIBERNATION 



The theories of hibernation can, perhaps, be divided into three categories though 

 none can be separated completely from the others. The first theory is not widely 

 accepted, but occasionally appears in the literature. ^"^ According to tliis theory, mam- 

 mals that hibernate are primitive, have poor temperature regulation and behave 

 physiologically like the poikilothcrmic lower vertebrates. Hence, when it is cold, 

 hibernators cannot resist the drop in temperature and therefore hibernate. \Ve hope 

 that those who have struggled thus far in this review will agree that the hibernators 

 do not react to cold as do reptiles and amphibians. Except for the l)ats, liibernators 

 can maintain the homeothermic state indefinitely,^''- and all mammals in hibernation 

 remain primed, as it were, so that an adequate stimulus may trigger the complex 

 waking ])rocess. This is more a specialization of the homeothermic state than a 

 reversion to the poikilothcrmic one. 



