Etiology of keratogenic metaplasia in the chorioallantoic membrane.

The effects of elevated O(2) and CO(2) concentrations on the occurrence of experimental keratogenic metaplasia in the chorion of the chick embryo were examined. Exposure to oxygen resulted in advanced keratinization of the chorion; carbon dioxide at elevated concentrations, in mixtures with air or oxygen, repressed the appearance of metaplastic changes, and the chorion retained its respiratory characteristics. The evidence reported here suggests that reduction of the CO(2) content in the gaseous environment of the chorion is causally contributory to the onset of the metaplastic events.