344 ARTIFICIAL INCUBATION 
the infertility of the eggs, dead germs, germs apparently sticking 
to the shell, and cracked eggs (Tig. 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. 
Fig. 162.—Eggs seven days in the incubator as seen when tested. A, Dead germ; 8, 
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 } 2 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. 
