INCUBATION 



93 



Moisture in Incubators. During incubation a part 

 of the water in an egg is evaporated, and as the moisture 

 content of the eggs grows less, the air cell becomes 

 larger. This is indicated by the size of the air cell. 

 The air cells differ under hens and in incubators in 

 the same room; they are not alike under different 

 hens, and they differ under the same hens and in the 

 same machines. The greater part of the moisture in 

 an egg disappears as the hatching period approaches, 

 and consequently the air cell becomes larger in size and 

 acts as a cushion, or filler, that prevents the embryo 

 from flattening out inside of the egg. The normal size 

 of air cell at different stages of incubation is shown 

 in Fig. 2, in which the numbered lines 

 refer to the size of the cell as seen 

 on the fifth, tenth, fifteenth, and nine- 

 teenth days. An egg loses about / 

 8 gr. of weight per day during the I 

 first 18 da. of incubation, the loss \ 

 being due mainly to evaporation. As 

 this loss occurs, the shell linings, or 

 the inner and outer membranes, sepa- 

 rate. This separation usually occurs 

 at the large end of the egg, where the 

 air cell is located. 



Notwithstanding the fact that the air cell is normally 

 located at the larger end of the egg, other air cells 

 may form on the side of eggs that are not turned for 

 several days prior to incubation or during the incu- 

 bation period. 



The normal mean relative humidity of the air under 

 the hen on the nest is about 60. More moisture than 

 this is not needed, and good hatches may be had with 

 less. Hot air evaporates moisture and enlarges the air 

 cells of the eggs. When the air cells are smaller than 

 normal, they may be enlarged by more ventilation and 

 less moisture. If moisture is lacking inside the egg 

 chamber, it must be supplied in some way or the success 

 of the hatch may be impaired. 



FIG. 2 



