Hedgehogs seem not to suffer water loss during hibernation or hypothermia probably through water shifts from the interstitium to the cells and/or protein catabolism in tissues. 2. Higher potassium concentrations were retained in hedgehog's tissues, sodium and chloride ions rose in plasma, but ionic gradients were slightly affected. Probable reasons for increased calcium, magnesium and inorganic phosphorus were discussed. 3. Changes recorded during late fall indicated the predisposition of animals to hibernate, while changes during spontaneous and full arousals showed a reversed phenomenon in the hibernation cycle. 4. Artificially hypothermic animals in summer showed results similar to those of naturally hypothermic in winter, although lower in magnitude, suggesting a specific role of temperature in regulating the hibernation cycle.
