The Gaseous Environment of the Chick Embryo in Relation to Its Development and Hatchability

TESTING an assumption that the developing chick embryo may have different requirements at different stages of incubation, four previous reports of this series (Taylor et al., 1956; Taylor and Kreutziger, 1965; 1966; 1969) have demonstrated a progressive increase in tolerance to higher levels of CO2 to the end of the 16th day of incubation. A fluctuating response to high O2 levels was observed. An early tolerance was followed by a decreased resistance, then by a reversal of trend toward a very high resistance in the 13-16 day period. Responses to low O 2 levels were within a very narrow range and without a significant trend. The final days of incubation are normally characterized by the highest levels of mortality of chick embryos. The present report involves results of various gassing levels for the two 4-day periods of 17-20 and 18-21 days respectively. During these days the chick embryo undergoes critical…