344 ARTIFICIAL INCUBATION 



the infertility of the eggs, dead germs, germs apparently sticking 

 to the shell, and cracked eggs (Fig. 162). 



The size of the air cell, as previously stated, will vary with 

 the period of incubation and the amount of ventilation; if it appears 

 too large or too small, steps to correct this should be immediately 

 taken. If the air cell is too large, the moisture in the air must be 

 increased to lessen evaporation, and if too small, evaporation 

 must be promoted by increasing ventilation. Air cells not prop- 

 erly located at the larger end of the egg are due either to the fact 

 that the eggs were kept too long in one position before being put 

 in the machine, or to improper turning prior to the seventh day. 



\ 



''* / 



? A \ /B 



FIG. 162. Eggs seven days in the incubator as seen when tested. A, Dead germ; B, 

 living germ; C, infertile egg. 



An egg which appears to be absolutely clear or translucent 

 without a dark spot with converging lines is infertile. All such 

 eggs should be plainly marked and put in a separate place. These 

 can be profitably used for chick feeding, by boiling them hard 

 and feeding them separately or mixed with mashes. White- 

 shelled eggs, if tested out on the fourth or fifth day, may be safely 

 used for baking purposes. The normal egg at this time will have 

 a clearly defined air cell; the germ will be noted about one-third 

 of the way from the large end, looking like two dark spots lying 

 close together, one a trifle larger and darker than the other; radiat- 

 ing from the germ will be seen numerous dark lines, crossing and 

 recrossing, which are the veins of the embryo. If the germ is not 

 readily detected, it can be brought to the surface by rotating the 

 egg slightly. At this time an infertile egg, especially in a strong 

 light, will show a slight dark area in the centre, which is yolk. 



