The significance of changes in the temperature of the skin and body core of the chicken in the regulation of heat loss.

1. The relationship between the temperatures of the hypothalamus, colon and skin and the control of heat loss mechanisms at ambient temperatures from 20 to 40 degrees C has been studied in unanaesthetized chickens.2. The temperatures of the core and feathered skin varied by not more than 5 degrees C throughout the full range of ambient temperature but the comb, shank and toe varied by up to 20 degrees C and exhibited wide fluctuations in constant environmental conditions.3. At an ambient temperature of 26-27 degrees C, the fluctuations ceased at all of the naked skin sites and there was evidence of a concurrent decrease in the tissue insulation of the extremities. No such change could be detected in the feathered skin.4. Analysis of the various body temperatures suggested that the onset of thermal panting was consistently related to the increment in hypothalamic temperature and that this relationship was influenced both by the peripheral and extra-cranial deep body temperatures.