EGGS AND INCUBATION 497 



cared for in most incubators. Openings in the bottom, 

 sides, or top permit fresh air to enter and impure air to pass 

 out. If there are openings in the top of the machine, much 

 more moisture must be supplied in the egg chamber, for 

 there will be considerable moisture carried out of the machine 

 with the warm air. If there are no openings in the top of 

 the incubator, the moisture in the eggs will be conserved; 

 but, in order to supply sufficient oxygen to the developing 

 embryos, there must be a system of ventilation that will 

 circulate the air inside the incubator so that the light odors 

 as well as the heavy gases will be dispelled and replaced with 

 a certain amount of fresh air. As a rule, the amount of 

 ventilation should be increased as the hatch progresses. 

 Late hatches require more ventilation than the earlier 

 hatches. The best guide as to the moisture requirement is 

 the egg itself. About two thirds of the egg content should 

 be occupied by the embryo on the nineteenth day. If too 

 much moisture is supplied and too little ventilation allowed, 

 the chicks will hatch with considerable irregularity and will 

 not dry off with a soft, smooth down. If proper ventilation 

 and moisture conditions have prevailed, the chicks will hatch 

 out with uniformity, with a clean, soft down. 



Turning and airing the eggs. Turning and airing the 

 eggs is necessary for the production of strong, vigorous 

 chicks. The hen on the nest turns the eggs with her feet 

 several times a day. Turning insures an even development 

 of the embryo and prevents any parts from adhering to the 

 inside of the shell. The necessity for turning is apparent 

 from the third to the eighteenth day of incubation; but, in 

 those incubators that have automatic turning devices which 

 permit the eggs to be turned without opening the machine, 

 it may be desirable to turn the eggs from the second to the 

 nineteenth day. There is no advantage in extending the 

 time, if the machine must be opened and the egg tray re- 

 moved in order to turn the eggs. Airing the eggs is a better 



