HIBERNATION IN MAMMALS— LYMAN and CHATFIELD 99 



less and concludes about three liours later with a fully awake and active animal with 

 a normal homeothermic body temperature. Although the waking process is slow to 

 start, once well under way it evidently proceeds to completion in all species of 

 hil)crnators. Certainly in the case of the golden hamster only death can stop the 

 animal from struggling to regain its homeothermic temperature. All evidence shows 

 that the arousal process is a highly coordinated physiological effort,^^' ^-' ^^' °*> ^°' 

 lis, 123 jj^ ^vhich the animal generates a maximum amount of heat in a minimum of 

 time. In spite of this, many investigators have considered the early part of the wak- 

 ing process as physiologically the same as the deep hibernating state. In our opinion 

 nothing could be further from the case, and failure to recognize this has resulted in 

 many erroneous observations in the past. 



The process of arousal consists of a series of precise physiological events which 

 may be studied with relative ease, but this has been the most neglected phase of 

 hibernation until recently. In general, the process is evidently similar in all terres- 

 trial hibernators, but we will use the golden hamster as an example as we are most 

 familiar with it. 



When the hamster starts to arouse from hibernation at an environmental tem- 

 perature of 5° C, the first visible change is a cessation of the periods of apnoea 

 which are typical of deep hibernation. Except for fine, slow waving of the vibrissae, 

 no other muscular movement can be seen. Within the first twenty minutes the respir- 

 atory rate may increase to 10, though the body temperature shows no measurable 

 rise. At the end of 90 minutes, the cheek-pouch temperature has increased to about 

 10° C. and the respiration is up to 35 and regular.^^' If the animal is on its side, 

 it begins to paw the air feebly, first with the front feet and later with the hind feet. 

 After about two hours, the cheek-pouch temperature has increased to as much as 

 19' C, the respiration to 100, and the animal reacts refiexly to mild stinudi. Thirty 

 minutes later the temperature is about 30° C, the respiration is above 100 and very 

 irregular and the animal makes uncoordinated efforts to stand. From 150 to 190 

 minutes after the initial stimulus the cheek-pouch temperature rises to 36 or 37° C. 

 During this time the animal is apt to shiver violently and its movements become 

 increasingly better integrated. At the end of 190 to 210 minutes after being dis- 

 turbed the animal is fully awake, with a temperature throughout the body of 

 37-38° C. (fig. 12). 



Circulatory changes. If the temperature changes in the cranial and caudal parts 

 of the body of the waking hamster are plotted against time, it may be seen that the 

 cheek-pouch temperature shows a measurable rise about 20 minutes after the animal 

 has been disturbed.^' Shortly after this, the temperature of the cranial portion of the 

 body rises rapidly, reaching the homeothermic level in a total of about 170 minutes. 

 The temperature of the caudal part of the body lags behind that of the cranial por- 

 tion, so that near the mid-point of the waking process the cranial portion may be 

 20° C. warmer than the caudaP-^ (fig. 13). Soon thereafter the temperature of the 

 caudal portion rises rapidly and reaches the temperature of the cranial in a total 

 time of about 200 minutes. Similar changes as arousal progresses have been de- 



§§ The term "cheek pouch temperature" has evidently caused some confusion. (See E. F. 

 Adolph and J. Richmond, J. Appl. Physiol. 8: 48, 1955.) It was previously explained'"'' that the 

 cheek pouch of the hamster is so large that it reaches over the scapular region. Cheek pouch 

 temperature is therefore the temperature of the thorax rather than that of the head. 



