1. (Also called acclimation. ) The process by which a living organism becomes adapted to a change of climatic environment. There has been a growing amount of research on the acclimatization of man to extreme environments such as polar and tropical regions and high altitudes. These studies are directed toward 1) determination of the internal physiological changes or skin changes produced by exposure to new climates, 2) determination of criteria for preselection (i. E. , selecting the most adaptable type of man for a particular climate), and 3) development of external means of aiding adaptation (e. G. , preconditioning, and modification of habits, diet, and clothing). As to usage, “acclimatization” has long been considered to be equivalent to “acclimation. ” In some quarters, however, a fine distinction is drawn by calling “acclimation” a purely natural process (or state), and “acclimatization” a process (or state) influenced by human agency. The recent trend, at least in the United States, is to use “acclimatization” as the all-inclusive technical term, and to leave “acclimation” (which never was accepted in Great Britain) to more or less loose popular usage. 2. The state or degree of adaptation to climate.