The circadian rhythms of heat production and its discharge are considered to be involved in generation of the body temperature rhythm. Daily changes in gluconeogenesis and other phenomena associated with energy metabolism are generated in close relation with food intake. Rats generally take more than 70% of their daily food intake in the dark period. In this case, the rat ate more than 90% of its daily food intake in the dark period. It has been shown that under physiological conditions a large portion of water intake in rats and dogs takes place in relation with food intake, especially during and immediately after food intake. In accordance with the appearance of sleep-wakefulness rhythm, milk drinking behavior shows initially free-running ultradian rhythm, followed by free-running circadian rhythm. W. I. Cranston and W. Brown reported that although the blood volume also showed a circadian rhythm, its amplitude was so small that it could not be responsible for the circadian corticosteroid rhythm.