Abstract
Compensatory responses to homeothermlc challenges are characteristic of all adult mammalian species (Hart, 1964; Irving, 1964; Brengelmann and Brown, 1965). Indeed, even unicellular and poïkilothermie metazoan animals are capable of altering their thermal range through enzymatic adaptations (see review by Smith and Hoijer, 1962). This phylogenetic relationship lead Smith and Hoijer to conclude that nonshivering thermogenesis was apparently an "intrinsic cellular capability" of all tissues and that the chemical regulation of heat production In the tissues of homeothermlc animals was implicitly controlled by an "elaborate matrix of impinging physiochemical mediators."