Abstract
Hibernation was induced in Columbian ground squirrels by placing them in refrigerated cages equipped with urine‐collection pans. On arousal, urine and blood were collected from each animal, which was then allowed to reenter hibernation. After several days the animal was sacrificed and bladder urine and another blood sample were taken. In addition, four active non‐hibernating ground squirrels were placed in a cage at room temperature with neither food nor water. Urine was collected at 9 and 26 hours and blood was collected at 0 and 26 hours. Although only seven of ten hibernating squirrels had a higher blood‐urea level when sacrificed than during the previous arousal, the other three had very high levels in the arousal period and probably further excreted urea before entering hibernation. When total body urea was calculated on a body weight basis, all except one animal showed a greater level of urea during hibernation than in the previous arousal. During their period of dehydration, the non‐hibernating summer squirrels showed a marked decrease in blood urea. The osmotic concentration of the urine from these squirrels was due less to urea than that excreted during arousal by hibernating squirrels. Thus, it appears that urea accumulates in the blood during hibernation and is excreted in the urine during arousal.