testing table. It consists of a
table the same width as an incubator tray and longer than the tray. In
the table there is an opening the size of a row of eggs and beneath this
are placed several electric light bulbs with reflectors back of them so
as to throw the light up through the eggs. By sliding the tray along the
table each row of eggs is brought over the lights and their condition
can be quickly noted. At this test all the infertile eggs are taken out
as well as any eggs in which the germs have died. The infertile eggs
after a careful retest are then packed in cases and sent to market where
they are usually sold to bakers as tested eggs. While no second test is
made of the eggs left in the machines the experienced incubator operator
is constantly on the watch for and is constantly removing any eggs which
die at a later time. To the experienced eye the color of the egg
indicates that it has died as it takes on a sort of pinkish or darkish
tint. Duck eggs after they die will spoil very quickly and must be
removed promptly as the odor which they throw off is very strong and
will prove harmful to the other eggs. The inexperienced operator can
readily locate dead eggs by smelling over the tray.
[Illustration: FIG. 21. Interior of house for breeding ducks. Notice the
heavy bedding and the feeding track. (_Photograph from the Bureau of
Animal Industry, U. S. Department of Agriculture._)]
[Illustration: FIG. 22. Incubator cellar on large duck plant. Trays of
eggs set out to turn and cool. (_Photograph from the Bureau of Animal
Industry, U. S. Department of Agriculture._)]
_Turning the Eggs._ The eggs are neither turned, cooled nor otherwise
disturbed after they are put in the incubator until after they are
tested on the fifth day. From this time on they are turned twice a day,
morning and night, until they begin to pip.
_Cooling the Eggs._ There is a considerable difference in the practice
of incubator operators with regard to cooling. No cooling should be done
until after the first test. After this some incubator men cool the eggs
by dropping the doors of the machine. Others take the trays of eggs out
and put them on top of the machine. Cooling is usually done once a day.
The amount of cooling which the eggs require seems to vary greatly and
here again the judgment of the operator comes into play. About the best
general rule which can be given is that the eggs should be cooled until
they do not feel warm to the face but they should never be cooled to