The relation between spontaneous activity, metabolic rate and the 24 hour cycle in mice at different environmental temperatures.

1. Oxygen consumption rates and levels of spontaneous activity were recorded simultaneously for mice, both singly and in groups, over 24 hr periods at temperatures ranging from 8 to 37 degrees C.2. There was marked 24 hr variation in both metabolic rate and activity, with maxima during the night; the amplitude of the variation diminished at the lower environmental temperatures.3. At 28-33 degrees C environmental temperatures, increased activity was associated with an increased oxygen consumption rate.4. At 8 and 15 degrees C, increased activity was accompanied by only a small increase in oxygen consumption.5. These results show that thermogenesis from spontaneous activity can take the place of thermoregulatory heat production in the cold.