Acclimatization to heat and cold

A fall of the rectal temperature, the skin temperature and the pulse rate can be detected in human subjects after a few days, or even a number of hours, in a hot environment, and this was considered to be a sign of acclimatization to heat (Bean & Eichna, 1943; Robinson, Turrell, Belding & Horvath, 1943; Eichna, Bean, Ashe & Nelson, 1945), but definite signs of acclimatization to cold were not obtained after repeated or continued experimental exposures to low environmental temperatures (Adolph & Molnar, 1946; Horvath, Freedman & Golden, 1947; Stein, Eliot & Bader, 1949), although a few authors have described minor signs of adaptation (Scott, Bazett & Mackie, 1940; Glickman, Keeton, Mitchell & Fahnenstock, 1946). The present investigation was planned to show whether acclimatization to cold did exist, and it also offered an opportunity of studying two further problems. (1) How were the movements of blood between the inside of the body and the extremities which were shown to accompany changes of the environmental temperature (Glaser, 1949b) affected by continued exposures to heat and cold? (2) Was acclimatization to heat and, if its existence could be demonstrated, acclimatization to cold modified by frequent changes of environmental temperature?