Abstract
Extractions of tissues of chick embryos were tested for identification of acetylcholine (ACh) and the quantitative changes in ACh during embryonic development from the 2nd to the 12th day of incubation were detd. No positive correlation was found between the development of ACh in the chick and the development of reflexes and of the nervous system. The results were discussed with reference to their bearing on the theory of chemical transmission, and the need for more critical expts. was emphasized.