A woodchuck given an amount of insulin sufficient to produce profound hypoglycemia loses its power of temp. control, and if placed in a cold environment passes into a state of artificial hibernation. The animal becomes poikilothermic and is unable to shiver or to execute spontaneous movements; consciousness is lost, as is sensibility to painful stimulation, and the metabolic rate is greatly decreased. The convulsions associated with insulin hypoglycemia do not occur. When glucose is injected, shivering begins almost immediately; the temp. rises at a rapid, though variable, rate; and the animal returns to normal. Hypoglycemia thus seems to be an important factor in the mechanism of hibernation.