92 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



A 12 J* C 100 w« T l»ec 



B I5»* 

 C 18.9* 



zta 

 C 228* 



F 23S* 

 6 it.T 

 H 29.4^ 



2. J 



Fig. 8. — The electrocorticogram of an arousing hibernator at increasing cortical temperatures. 

 Absence of definite electrical activity until record D, temperature 20° C. In records E, F, and G, 

 increasing number of slow waves which eventually become grouped into bursts in record G. 

 Onset of activation pattern in record H, at a still higher temperature. Record I, 1 minute after 

 a subsequent injection of pentobarbital sodium. Note replacement of activation pattern with 

 typical burst, similar to that seen in the colder unanaesthetized cortex in record G. J, 9 minutes 

 after the injection. No cortical activity. Small waves are artefacts from the EKG. 



as the animal was subjected to chilling, foimd that the neural component of this 

 response, which presumably indicates conduction in the auditory nerve, could not be 

 recorded below body temperatures of 18° C. That the golden hamster while hiber- 

 nating is functionally deaf is borne out by the fact that we have never been able 

 to arouse a hibernating hamster by the stimulus of sound. The woodchuck, on the 

 other hand, which shows an evoked cortical potential in response to a sound stimulus 

 at cortical temperatures as low as 7° C.^'^ probably does respond to environmental 

 sound even in deep hibernation, as was indicated by the earlier researches of 

 Benedict and Lee'^^ and apparently the same holds true for the Eiu'opean ground 

 squirrel^^ (fig. 7). 



Acid-base balance. As early as 1896, Dubois*'- reported a higher total COo in the 

 l)lood of hibernating marmots than in awake animals and used this finding as a basis 

 for his autonarcosis theory of hibernation. This high total COo has been confirmed 

 many times.^°' ^^' ^-' ®^' ^^' ^^ Endres^^ and Stormont, et al.^" reported a lower pH 

 in the blood of hibernating ground squirrels. The high total CO2 led to the con- 

 clusion that the respiratory center undergoes a loss of sensitivity during hiberna- 

 tion.'**' ^°' °^ This conclusion, however, disregards the well-established fact that the 

 respiratory activity depends primarily on the COo tension (pCOo) and possibly the 

 pH rather than the concentration of total COo in the blood. Stormont, ct al.^' 

 were apparently the first to recognize this and calculated the pCOo of the blood of 

 hibernating ground scjuirrels from pH and COo determinations but admitted that 



