Gas exchange of the fertile hen's egg: components of resistance.

The resistance to diffusion of respiratory gases falls by 50% from day 10 to day 18 in the incubating fertile hen's egg (Temple and Metcalfe, 1970). We have calculated the change in the components of this resistance with respect to incubation age. The egg shell resistance remains unchanged. The chorioallantoic membrane (including capillary endothelium) resistance decreases dramatically from day 10 to day 14 and then remains relatively unchanged. The resistance offered by the blood is unchanged from day 10 to day 12, it decreases by day 14 due to an increase in oxygen capacity and continues to decline at days 16 and 18 because of the combined effects of a continued increase in oxygen capacity and an increase in capillary volume.