8 
Farmers' Bulletin 1106. 
heat to escape and to avoid the risk of fire. Special care should 
always he exercised in using kerosene lamps to prevent fire. To 
prevent further possibility of fire, a wooden box may be used in 
place of a pasteboard one, and if desired, the opening through which 
the chimney extends may be lined with tin or some fireproof material. 
Electric or gas lamps may be used in a box with a hole, slightly 
smaller than an egg, cut in the side of the box and at the same level as 
the light. The eggs may also be tested by sunlight or daylight, using 
a shutter or a curtain with a small hole 
in it for the light to shine through. 
The testing should be done in a dark 
room. To test the eggs, hold each egg 
with the large end up, so that the size 
of the air cell may be seen (see fig. 5), 
as well as the condition of the embryo 
or germ. An infertile egg when candled 
looks perfectly clear, the same as a 
fresh one, while a fertile egg shows a 
dark spot, known as the embryo, with 
a mass of little blood veins radiating 
in all directions. If the germ is dead 
and the egg has been incubated for at 
least 48 hours the blood settles away 
from the embryo toward the edges of 
the yolk, forming in some cases an 
irregular circle of blood known as a blood ring. Eggs vary in this 
respect, some showing only a streak of blood. 
All infertile eggs and those with dead germs should be removed at 
the first test. Eggs with dead germs soon decay and give off a bad 
odor if allowed to remain. Infertile eggs make good feed for young 
chickens (see Farmers’ Bulletin 1108). 
At the second test (on the fourteenth day) the eggs containing 
strong, living embryos will be dark and well filled up, showing a 
clear, sharp, distinct line between the air cell and the growing embryo, 
while eggs with dead germs will show only partial development and 
lack this clear, distinct outline. 
Fig. 5.—Diagram showing the air cell of a 
egg on the seventh, fourteenth, and nine¬ 
teenth days of incubation. 
HATCHING. 
The period of incubation for hens’ eggs is 21 days. Usually some 
of the eggs hatch in the evening of the twentieth day; it sometimes 
happens, however, that the hatch will run over the twenty-first day, 
especially during cool weather. 
When the eggs begin to hatch, the hen should be confined and not 
disturbed until the hatching is complete unless she becomes restless. 
In such case it is best to remove the chicks which have been hatched 
and keep them in some warm place until the hatch is completed. 
Then return all the chicks to the mother. 
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1920 
