Daily observations on each of over one hundred individuals of C. lateralis by a special technique indicated that no animal remains continuously in the hibernating state longer than approximately 16 days (at an environmental temperature of 32° F). The arousals were more frequent at the beginning (i.e. in the autumn) and the ending (i.e. in the spring) of the whole hibernating period, than during the middle of this period (December and January). Adult males were found to arouse more frequently than did adult females or the juveniles of either sex. Preliminary data indicate that arousals are more frequent the higher the environmental temperature (up to 70–75° F), Observations on 12 C. columbianus, 9 C. tridecemlineatus, and 28 Glis glis indicated maximum continuous hibernation periods of 19, 12 and 33 days, respectively, at an environmental temperature of 32° F; C. richardsonii did not hibernate under our laboratory conditions.The trigger which starts each arousal is not known. Food and water intake during an arousal is not necessary, nor is defecation. Urination, however, takes place during every arousal. The observations strongly suggest that the urine voided was formed only while the animal was in the active homothermic state. It is suggested that it is the accumulation of metabolic end products which constitutes the stimulus for an arousal.

The state of torpidity (hibernation), the food consumption, and the weight of a number of C. lateralis were recorded daily, weekly, and weekly, respectively, for periods up to 2 years. At ambient temperatures of 32" F , 70' F , and 95-100' F and under constant lighting conditions, all animals displayed an approximately 1-year cyclic variation in weight which roughly paralleled the consumption of food. Under these constant conditions of light and temperature the animals subjected to 32O F and 70" F hibernated, i.e., their body temperature dropped nearly to the ambient and they became torpid. The body temperature of animals kept a t 95-100' F could not drop and these animals did not become torpid.Hibernation could not be induced by removal of food but was greatly prolonged if food was not present in the cages a t the time the whole hibernation period was ending. The onset of hibernation could be changed only slightly by changing the day lengths. Hibernation was possible only a t a specific stage of the weight cycle. The length of the weight cycle was shortened by exposure to an ambient temperature of 95-100" F. By manipulation of the length of the exposure to the high temperature it was possible to have animals hibernating in summer and active in winter. I t was not possible to produce a similar shift in the phase of the weight cycle, and hence of hibernation, by changing the lighting conditions.

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