The Avian Egg: In vivo Conductances to Oxygen, Carbon Dioxide, and Water Vapor in Late Development

Summary

In vivo measurements of both O₂ and water vapor conductances(${\text{G}}_{{\text{O}}_{\text{2}} }$ and ${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$) were made at 38°C on the same hen’s eggs between days 12 and 18 of incubation. Neither ${\text{G}}_{{\text{O}}_{\text{2}} }$ or ${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$ changed systematically during this phase of incubation. Average ${\text{G}}_{{\text{O}}_{\text{2}} }$ (cm³/day/torr) was 12.60 ± 0.30 (S.D.); average ${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$, 15.26 ± 0.51; ${\text{G}}_{{\text{O}}_{\text{2}} }$/${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$= 0.83. In vivo determination of ${\text{G}}_{{\text{CO}}_{\text{2}} }$ and ${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$ in a second group of eggs gave values of 9.22 ± 1.54 and 14.60 ± 0.65, respectively; ${\text{G}}_{{\text{CO}}_{\text{2}} }$/${\text{G}}_{{\text{H}}_{\text{2}} {\text{O}}}$= 0.64. The conductance ratios agree closely with the binary diffusivity ratios (in air or N₂) of the gases in question. We conclude that O₂, CO₂, and water vapor diffuse between environment and air cell of the chicken egg via the same diffusion path, whose chief resistance lies in the shell itself. The outer shell membrane offers little resistance in vivo to passage of gas molecules.