HIBERNATION IN MAMMALS— LYMAN and CIIATFIELD 107 



ik'ld'--- were able to show that the cheek-pouch temperature of hauisters eviscerated 

 (luring hiberuatiou iucreased iu the uoruial mauuer to ?)2° C, aud iu later experi- 

 nu'iits with improved techni(|ue. Lyman and l.educ"^- demonstrated that the tem- 

 perature could reach the homeothermic level of 57° C. in this preparation. It was 

 concluded that the experimental procedures used to isolate the liver, on which Dubois 

 based his hypothesis, caused acute portal stasis or pooling- of the blood in the 

 splan.-lmic bed,i''' and that it was tliese del)ilitatino- effects whicli impaired the 

 warming- process. 



Altliough no nuiscle action potentials were detectable in the hibernating- golden 

 hamster except when the animal took a breath, action potentials appeared as soon 

 as the animal started to awaken.^-^ If the animal was momentarily touched or 

 otherwise disturbed, these action potentials increased greatly in amplitude and so 

 continued for a few seconds after the stimulus was removed (fig. 20). In spite of 

 action potentials, there were no noticeable muscular movements at this time except 

 for an occasional respiration. As the warming process progressed, the muscle action 

 potentials increased in amplitude and frequency and finally became continuous. Un- 

 published observations indicate that very similar conditions obtain in the ground 

 squirrel and woodchuck, except that occasional muscle action potentials may be 

 recorded in deep hibernation as these animals make slight changes in their position. 



Total curarization of the hibernating hamster caused marked slowing of the 

 warming process, thus demonstrating the importance of the action of skeletal muscle. 

 Remarkably enough, however, some warming took place even in the eviscerated, 

 curarized animal. The heart may be implicated as an alternative source of heat for 

 heart rate increased before any rise in body temperature, and slowing of the heart 

 by anoxia (which acts reflexly via the vagus nerve) or by veratrosine, caused a drop 

 in body temperature.''^ During arousal the heart of the hamster is beating very 

 rapidly against a high peripheral resistance and, as Starling and Visscheri'^s and 



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STIM STOP 



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4 



Fig. 20. — Ink writer records. Record no. 1 shows muscle action potentials and heart rate 

 recorded 25 seconds after hibernating animal was first disturbed. At point marked "stim." 

 animal was touched with a pencil. At "stop" the stimulus was removed. Note immediate increase 

 of action potentials with stimulus and continued activity after stimulus was removed. Heart rate 

 is 12 per minute. Records no. 2-5 illustrate the increasing heart rate and spontaneous muscle 

 action potentials of animal waking from hibernation. Heart rates are 27, 2Z, 72 and 108 respec- 

 tively. 



