MICROBIOLOGY OF HIBERNATION IN GROUND SQUIRRELS 



portant in determining when they will enter or emerge from the 

 hibernating state. It would appear that the animal receives few, if 

 any, clues from its environment, such as photoperiodicity or tem- 

 perature (Pengelley and Fischer, 1957). 



Ground squirrels and other mammalian hibernators undergo 

 natural awakenings from time to time during the hibernating period 

 (Lyman and Chatfield, 19 55), Kays er (1960) reported that the average 

 period of continuous hibernation in ground squirrels is about 21 days. 

 In our work we have been somewhat less successful. The cause of 

 the periodic arousals inundisturbed animals has yet to be explained. 



For a more complete survey of the physiology of mammalian hi- 

 bernation, the reader is referred to the recent publication edited by 

 Lyman and Dawe (1960). 



MATERIALS AND METHODS 



Arctic ground squirrels ( Spermophilus undulatus), adult animals 

 of both sexes, were captured in the Paxson Lake area of central 

 Alaska during the month of August. They were housed individually in 

 metal cages equipped with removable wire mesh floors and catch 

 pans. Their diet consisted of apples, carrots, and Labena pellets 

 (Ralston Purina Co., St. Louis, Mo.). They were observed in the 

 colony for 2 months before the studies were initiated. Hibernation 

 was induced by placing the animals in a cold room at an ambient 

 temperature of 3° C ± 1° C for the bacterial work and 5° C ± 1° C 

 for the viral studies. These temperatures were maintained through- 

 out each ofthe respective investigations. The animals were observed 

 daily but not disturbed unnecessarily, because various stimuli may 

 trigger an arousal from the hibernating state. 



The primary explants of monkey kidney cells were obtained from 

 Shamrock Farms (Middletown, New York) and maintained on Eagles 

 basal medium with Hank's balanced salt solution (BSS), HeLa mono- 

 layers were prepared from the S-3 clone, kindly supplied by 



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