Exposure to cold with retention of protective reflexes leads to a gain of intracellular water throughout the body. When, however, the C.N.S. becomes so chilled as to cause general neuro-muscular depression, the effect on the hypothalamus is to abolish the reflex responses to cold, which process includes a reversal of the water shift with increased extra-cellular fluid. Subcutaneous edema tends to occur and is augmented on rewarming the animal, which procedure increases greatly the hydration of blood, at least relatively.