The influence of hypothalamic temperature and ambient temperature on thermoregulatory mechanisms in the pig.

1. Two types of temperature fluctuation have been recorded from the preoptic region of the conscious pig. One, which is associated with arousal or movement, and another, which is related to rhythms in respiration and blood pressure.2. When the pigs were subjected to infra-red irradiation at various ambient temperatures it was found that there was no precise temperature of the preoptic region at which the respiratory frequency increased.3. Local heating of the preoptic region was effective in increasing the respiratory frequency only when the ambient temperature was above 30 degrees C.4. Even when both the peripheral temperature and central temperatures were increased there was a delay of several minutes before the onset of panting.5. Cooling the preoptic region of the hypothalamus prevented the onset of panting in a hot environment, and reduced respiratory frequency in an animal which was already panting.6. Oxygen consumption was reduced in a cold environment when the preoptic region was warmed, and increased when it was cooled. No increase in oxygen consumption occurred when the hypothalamus was cooled in a hot environment.