VENTILATION 341 
air without too great a loss of moisture from the egg, due to 
evaporation. Evaporation of the fluid in the egg is influenced by 
the rapidity with which the air circulates through the egg chamber, 
and by the humidity of the air itself; hence the factors of ventila- 
tion and moisture are closely related. The proper ventilation of 
the incubator is very essential. 
There are three methods of ventilating the smaller or individual 
incubator. The first, and most efficient, is by the introduction of 
fresh air into the machine, the intake being at the lamp box and 
the pure air heated as it enters the machine. The second is by 
the use of small ventilators controlled by sliding valves which lead 
directly to the inside of the machine through the wall. The third 
is ventilation through the bottom of the incubator, the bottom 
being provided with openings or slits, and, in some cases, so con- 
structed that it can be let down. In some machines these three 
modes are combined, while in others only one or at the most two 
are used. Whatever the system used, there should be an abundance 
of fresh air passing slowly through the chamber, and this can be 
regulated by muslin or burlap curtains to cut off any draft. 
Evaporation and Moisture.—The real gauge of the ventilation 
is the evaporation which takes place within the egg in a given 
time; hence, one of the best means of ascertaining the exact rela- 
tion between ventilation and moisture is a study of this evapora- 
tion. It can be determined by testing or candling the eggs, and 
noting the increased size of the air cell. For instance, when the 
egg is first put into the machine the air cell is very small, being 
only about one-eighth of an inch in depth. Under normal con- 
ditions it will have increased on the third day to about one- 
quarter of an inch in depth, on the eighth day to about three- 
eighths, on the fifteenth day to about five-eighths, and on the 
nineteenth day to about three-quarters. This is caused by air 
penetrating the shell and taking the place formerly occupied ‘by 
the evaporated liquids. 
The evaporation which takes place in the normal egg during 
incubation has been determined as follows: One hundred eggs 
of average size will lose during the first five days of incubation 
8.28 ounces, during the next seven days 12.05 ounces, and 
during the next seven days 12.044 ounces. This shows the high 
degree of loss, and the loss becomes still greater as the hatch 
progresses. 
Many experiments have been conducted to determine the de- 
