The effect of ambient temperature upon post-natal changes in oxygen consumption of the guinea-pig.

1. The effect of thermal environment and administration of progesterone upon minimal oxygen consumption and thermal stability of the new-born guinea-pig has been investigated.2. It was found that the ambient temperature at which the new-born is reared does not influence minimal oxygen consumption although it modifies the response to cold.3. Thermal stability was decreased in animals raised in a warm environment.4. Minimal oxygen consumption per unit body weight during the neonatal period increased 25%, most of the increase taking place within 16 hr after birth.5. Decrease in the relative mass of brown adipose tissue was least in new-borns maintained at a high ambient temperature.6. Administration of progesterone did not affect oxygen consumption, body temperature and thermal stability of the new-born.