Abstract
Mammals regulate their internal environment within narrow temperature limits, even in the face of environmental temperature extremes. When a small mammal, such as a rodent, is exposed to cold winter temperatures or simulation of these conditions in the laboratory, there are two mechanisms which can be employed to regulate the internal temperature: 1) a decrease in heat loss from the body surface to the environment, or 2) an increase in the internal heat production. Both of these mechanisms are operative in the chronically cold-exposed animal.