Man is often exposed to a hot and humid environment. When he is normal and the environmental change is slow as with the seasons, hereadily adapts to the environment. The physiological alterations associated with acclimatization, although not completely understood, are remarkably effective. Inhabitants of the tropics show structural as well as physiological alterations in response to climate. The mechanisms whereby these structural alterations are produced are poorly understood. Even the economic, cultural, social, ecologic, and anthropologic effects of climate on man and civilization have been little studied. Their importance, however, is becoming more and more evident in view of an expanding population on a planet of fixed size. Recent African developments and the increasing political importance of countries located largely within the tropical belt have increased interest in the tropics. Furthermore, the exploration of space will certainly find man exposed to climatically stressful environments.
Most of the United States, particularly