DIURNAL PATTERNS OF METABOLIC VARIATIONS IN CHICK EMBRYOS

1. Continuous recordings of oxygen consumption were made in order to determine ontogenetic, daily, seasonal, temperature, and other relationships of metabolic variability in chick embryos.2. Statistical treatment involving linear regression analysis facilitated resolution of daily cycle forms and allowed various comparisons.3. The pattern of metabolic variation during days four and five has several peaks, but by days seven and eight a more markedly diurnal pattern appears. Day six appears to be an intermediate or transitional stage.4. Seasonal differences in the form of the daily cycle resemble those reported for other organisms.5. Lowering the temperature 5° C. does not affect the period length of the metabolic variations. A suppression of nighttime metabolism relative to daytime metabolism suggests the expression of a diurnal variation in temperature sensitivity.6. Initiation of incubation at different times of day does not result in different basic cycle forms.7. Results obtained with chick embryos are suggestive of a receptor system which is responsive to external time cues.