Circadian rhythms inMacacamonkeys (physical activity, temperature, urine and microfilarial levels)

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Abstract
Investigations were made on the 24 hr cycles of two Macaca irus monkeys under conditions of 12 hrs light/12 hrs dark, of continuous darkness and of continuous light. Under 12 hrs light/12 hrs dark, the physical activity of one of the monkeys lasted only 8–9 hrs. In both monkeys the body temperature began to start to rise before light (and activity) came on and it began to fall when they stopped. The urinary excretion of water, K+, Na+ and Cl‐ showed high rates during the light period with a maximum in the middle period. Under continuous light, the activity was as great as before but it was progressively postponed by 0.2 ‐ 0.6 hr/day. The temperature cycle and the urinary cycles were slightly postponed but otherwise amplitude of the temperature cycle was much diminished and the total volume of urine excreted and the range of the urinary cycles were diminished. One of the monkeys contained infections with two species of microfilariae. The cycles of these continued without gross or consistent change during continuous light and even during continuous darkness showing that there was persistence of the circadian rhythms to which the microfilarial cycles were oriented.