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Synopsis
Covering the whole shell or the shell over the chorio‐allantoic membrane with liquid paraffin resulted in the diffusion of oxygen through the shell over the air space before the onset of pulmonary respiration being reduced to a level insufficient to keep the embryo alive. During the parafoetal period respiratory exchange through the air space becomes progressively more important than that through the allantois with the result that the embryo can survive a blocking of the whole shell or allantoic shell during this period, provided that pulmonary respiration has been developed sufficiently and that the shell is pipped within a certain time limit. After pipping respiratory exchange can be effected by pulmonary respiration alone, without great danger to the embryo.
It was found that diffusion through the shell over the air space could be abolished, by a covering of liquid paraffin, for at least 2 days without causing the death of the embryo. On the other hand, increasing the gaseous exchange through the air space by drilling a hole through the shell did not improve hatch‐ability. It may therefore be concluded that the respiratory exchange through the allantoic shell is greater than through the air space shell up to the time of pipping.
By measuring directly the gaseous exchange through the shell over the air space and allantoic shell it was shown that the amount of the diffusion through the shell over the air space was in proportion to the total diffusion, at least until the onset of pulmonary respiration. After that moment the absolute as well as the percentage exchange via the air space increased. This was, however, attended by only a relative and not an absolute decrease in respiratory exchange through the allantoic shell.
The allantois did not begin to degenerate until pipping had taken place. Lung function then increased and soon took over completely the function of the allantois. As soon as the allantoic respiration had been practically abolished hatching activities started with the result that hatching often followed within half an hour.
