Effect of two gas mixtures on growth of the domestic fowl embryo from days 14 through 17 of incubation.

Eggs weighing 62.5 +/- 0.5 gm when fresh were incubated in air in a forced-draft incubator for 13 days during which time their shell conductance to water vapor (GH2O) was determined. Eggs whose shells represented the entire range of GH2O values present in the population were then incubated for a further 4 days in either air or an experimental gas mixture. Embryo dry weights were determined after a total of 408 hr of incubation to assess the affect of the experimental gas mixture on embryonic development. Embryo growth was found to be stimulated for all eggshell conductances by 4 days incubation in a 50% oxygen/50% nitrogen mixture. This suggests that the decrease in oxygen within the egg that occurs during development normally limits embryonic growth. Growth of the embryo was unaffected by 4 days incubation in a mixture of 17% oxygen/83% helium. This mixture reduced the carbon dioxide tension in the airspace but did not affect the oxygen tension relative to eggs incubated in air. It is suggested, therefore, that the carbon dioxide that builds up within eggs during incubation does not limit embryo growth.