086 w. V. :mayer and s. bernick 



lined ground squirrel. In t!ie present inxestigation the autliors have 

 examined histologically the effects of hibernation on the teeth 

 and on the surrounding bones and periodontium of a hibernating 

 animal. 



Hibernation is a relatively rare phenomenon. The term is correctlv 

 used to identify that metabolic state involving cessation of externally 

 observable activity and a marked lowering of the body temperature 

 of the homoiotherm. Though it is commonh' thought of as a phe- 

 nomenon of the high Arctic, it is in realit\' a temperate-zone phe- 

 nomenon, to judge from the geographic distribution of the animals 

 which actually hibernate. The phenomenon is limited to relatively 

 few genera of birds and mammals and is considered by the senior 

 author to be a highly stressful and relatively unsatisfactory method 

 of meeting environmental extremes, at least for the individual ani- 

 mal, although it is sufficiently effective for species survival. 



The selection of the Arctic ground squirrel as the hibernator for 

 use in these experiments is based on the facts that it is a large animal 

 readily kept in captivity and that it can be induced to hibernate 

 relatively easily. Mayer (1953a, 1953/?) has reported on the ecolog- 

 ical relationships of the Arctic ground squirrel and its patterns of 

 hibernation. Although in this paper such terms as "3 months in 

 hibernation" are used, it is to be understood that hibernation is not 

 a continuous process, operating from September until Mav in the 

 case of the Arctic ground squirrel, but rather a series of hibernations 

 from which the animal periodically awakens at roughly 3-week in- 

 tervals. Thus, a 3-month period of hibernation would undoubtedly 

 have included at least four such awakenings. 



The Arctic ground squirrels for this study were obtained from 

 Alaska and maintained in colonies in our laboratories. 



Materials and Methods 



The animals used for this study were Arctic ground squirrels 

 (CiteUtis undulatus) , ranging in age from 3 to 4:1 years. In captivity 

 they had been subsisting on a natural stock ration ( Purina ) supple- 

 mented with vegetables, such as lettuce, cabbage, carrots, or celery. 



Animals were sacrificed and the skulls removed, decalcified, em- 



