Ontogeny of DNA synthetic rhythms in chick (Gallus domesticus) liver.

1. The diurnal pattern of DNA synthesis and mitotic activity in neonatal (1-4-day-old) chick liver were investigated under various feeding and lighting regimens. 2. In the meal-fed chicks under the condition of light-dark cycle, DNA synthesis exhibited a 12 hr cycle; the peaks occurring at 9:00 and 21:00. 3. Fasting caused a gradual decrease in the 21:00 peaks. 4. The changes in the lighting regimen to 24 hr continuous lighting also caused a profound change in the DNA-synthetic pattern, suggesting a complex interplay of feeding and lighting regimens in the manifestation of the DNA-synthetic rhythm in neonatal chick liver.