Role of naso-buccal passages in thermoregulation in sheep.

1. Experiments with a face-mask in which the temperature of the air in the face-mask was raised to 40 degrees C while the ambient temperature in the chamber was maintained at 20 degrees C, resulted in a marked increase in respiratory frequency and a slight decline in carotid blood temperature of unshorn sheep. Partially shorn sheep showed only small respiratory responses.2. Localized infra-red irradiation of the naso-buccal area of unshorn sheep also resulted in an increased respiratory rate.3. It is suggested that the initiation of polypnoea during infra-red irradiation of the naso-buccal region and following rise in the temperature of the air in the face-mask is due to stimulation of warm receptors in the upper respiratory tract.4. Cooling the naso-buccal air in the face-mask to 10 degrees C after thermal polypnoea had been established at an ambient temperature of 40 degrees C resulted in a moderate decline of 30-40 respirations/min. This decline was attributed to the stimulation of cold receptors located in the upper respiratory tract.