IT IS NOW generally accepted that in mammals the essential heat-regulating mechanism of the central nervous system has a supraspinal localization; and numerous studies have proved conclusively that the functional integrity of the hypothalamus is necessary for normal temperature control. Shivering and panting, effective in raising or lowering the body temperature, do not occur if the connections between the hypothalamus and the remaining portions of the brain stem have been interrupted. Only isolated and ineffective fragments of these reactions can be elicited in animals with more caudally placed transections of the brain stem. Thus, Dworkin1 observed shivering in bulbospinal rabbits exposed to cold, and Macht and Bard2 evoked shivering and panting in mesencephalic and bulbospinal cats at extremely low and extremely high body temperatures. However, none of these animals was successful in combating the effects of changes in environmental temperature, and such responses, although they are interesting theoretically,