TIME REQUIRED FOR INCUBATION 321 
Time Required for Incubation.— 
Under normal conditions of tempet- 
ature and other factors, it will take 
the average hen’s egg twenty-one 
days to complete the process of in- 
cubation, beginning from the time 
the egg is subjected to 103 degrees, 
until the chick is entirely out of the 
shell. Under artificial conditions, 
there are causes which may vary the 
hatching time twenty-four hours 
either way from the normal. In arti- 
ficial incubation, the variation in 
temperature will materially decrease 
or lengthen the hatching period. A 
high temperature continued for a 
number of days will shorten the 
period, while a cool temperature ex- 
tending over a considerable time will 
often materially lengthen the hatch- 
ing period to as many as twenty- 
three days. It is an interesting fact 
that a variation of two or three 
degrees from thenormal temperature 
either way, providing the average 
temperature is normal, does not no- 
ticeably affect the hatch in any way. 
Varying amounts of moisture in 
the incubator also materially affect 
the time of hatching. A high humid- 
ity during the last week, and espe- 
cially during the nineteenth and 
twentieth days, will postpone the 
hatch as much as from twelve to 
twenty-four hours, but will usually 
result in a quick, uniform, high per- 
centage hatch. When managing the 
incubator, long periods of cooling 
will increase the hatching period. 
Under natural methods, the eggs 
-will hatch on the twenty-first day. 
21 
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16 
Fia. 152,—Manner of toe punching 
for baby chicks, showing sixteen com- 
binations, making it possible to identify 
sixteen different matings. 
