On the carbohydrate metabolism of pectoral muscle in the ontogeny of chicken.

1. Immediately after hatching, the pectoral muscle has a low glycogen content, and exhibits very low glycogen and high glucose and oxygen consumptions. 2. Drastic metabolic changes occur during the second day and again during the second week of life ("critical periods of the ontogenesis"); the above metabolic pattern is reversed. 3. The insulin sensitivity of the muscle is very low during these critical periods, and high between them. 4. The overall trend of metabolic ontogenesis in the pectoral muscle of the domestic fowl (non-flying bird) seems to have no functional but genetical determination.