The air space and embryonic respiration

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Abstract
Blocking the respiratory exchange through the shell over the air space by coating the shell with paraffin was attended by a sharp decrease in the oxygen content and a moderate increase in the carbon dioxide content of the air space. Before the parafoetal period the paraffin‐coated air space contained 6.4–8.5 per cent O2 and 7.2 per cent CO2. In normal eggs the composition of the gas mixture was 14.2 per cent O2 and 5.6 per cent CO2. During the parafoetal period the air space of paraffin‐coated eggs contained 4.6–6.5 per cent O2 and 7.3–7.7 per cent CO2 as compared with 9.0 per cent O2 and 6.6 per cent CO2 in the controls. Shortly before pipping the O2 content was 5.2 per cent and the CO2 content 9.1 per cent in the paraffin‐coated eggs and 8.6 per cent O2 and 8.1 per cent CO2 in the controls. It has been shown that the time of pipping is accelerated by a decreased O2 content as well as by an increased CO2 content in the air space. The stimulating effect of CO2, however, was about twice that of O2. The deviations from the mean pattern of gaseous exchange through the shell over the air space and the allantoic shell in normal eggs was linked with the duration of the parafoetal period. It was shown that the egg shells were pipped earlier when the respiratory quotient on the air space side was greater, and on the allantoic side smaller, than the mean. This relation was due to the fact that the parafoetal period was positively and linearly dependent on the O2 intake through the air space and the CO2 output through the allantois, but not on the CO2 output through the air space and the O2 intake through the allantois. It was shown that the differences between the eggs in the level of gaseous exchange were not the result of differences in egg shell porosity but of differences in the ability of the lungs to take up O2 and the allantois to give off CO2. After blocking the gaseous exchange through the shell over the air space about two‐thirds of the CO2 output and about one‐quarter of the O2 uptake originally established through this part of the shell appeared to be taken over by the allantois. The total O2 uptake therefore fell more than the CO2 output after this treatment with the result that the respiratory quotient rose. It was shown that the length of the parafoetal period in both normal eggs and eggs with a paraffin‐coated air space was dependent on the nature and magnitude of the gaseous exchange through the shell over the air space and allantoic shell during this period.

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