Basic to the drive concept is the principle of homeostasis, which refers to the body’s tendency to maintain a constant internal environment.

The healthy individual for example, maintains body temperature within a few degrees. Slight deviations from normal temperature set into operation mechanism that restores the normal condition. Exposure to cold constricts blood vessels on the body’s surface in order to retain the warmth of the blood, and we shiver which produces heat. In warm weather, peripheral blood vessels dilate to permit heat to escape, and perspiration has a cooling effect. These are automatic mechanisms designed to keep body temperature within normal range.