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Synopsis
The time at which pipping took place in eggs from a number of breeds and cross‐breeds was accelerated by an average of 7.6 hr by preventing gaseous exchange through the shell over the air space after 171/2–191/2 days of incubation. In contrast the time of pipping was delayed by an average of 6.0 hr when gaseous exchange by the same route was increased. The time of hatching, however, was not changed by either treatment. The period between pipping and hatching lasted therefore 20.1 hr in the eggs of which the shell over the air space was coated with liquid paraffin, 12.5 hr in the control eggs and 6.5 hr in the eggs with opened air spaces.
When the treatments were carried out at the onset of pulmonary respiration the parafoetal period lasted 3.7 hr in the paraffin‐coated eggs, 9.0 hr in the controls and 14.9 hr in the opened eggs. The period between the onset of lung ventilation and the time of hatching was 23.7 hr, 22.9 hr and 21.6 hr on average in the respective groups.
The inhibition of the gaseous exchange through the shell over the air space stimulated mainly or exclusively the process of pipping. It was shown that this stimulus is not effective until pulmonary respiration has been initiated.
The possibility was taken into account, however, that an inhibition of the gaseous exchange across the shell before the onset of lung ventilation could also have a slightly stimulating effect on this event.