The appearance of noradrenaline and adrenaline and the developmental changes in the their concentrations in the gut of the chick.

1. The times of appearance and the concentrations of noradrenaline and adrenaline were determined fluorimetrically in the gut of the embryonic and developing chick. 2. In the duodenum and jejunum, noradrenaline was detected in embryos on the 12th day of incubation. The concentration continued to increase throughout the embryonic stage and attained a maximum within 3 days of hatching. Afterwards, it decreased to about one-third of the peak level. No adrenaline was detectable in most stages of development. 3. In the rectum, noradrenaline was detected in embryos on the 12th day of incubation; both noradrenaline and adrenaline were invariably found on the 15th day of incubation. The concentrations of both amines fluctuated after hatching, but the amount of adrenaline was always approximately 40% of the amount of noradrenaline, except in the adult.