340 ARTIFICIAL INCUBATION 
oxygen than would be possible in the machine itself. The length 
of time for cooling depends upon the temperature of the room 
and the season of the year, and also upon the ventilation of the 
machine. It is impossible to lay down definite rules; but it is safe 
to begin cooling on the fifth day, and cool from four to five minutes 
in a room heated to about 60°. Do not let them cool any longer 
than the time required for turning, in a room which is much cooler 
than this. After the fifth day, the time for cooling should be 
gradually increased, until, during warm weather and in the latter 
¥ie. 160.—Interior view of incubator cellar. Operator turning and cooling eggs. Water 
is used on the floor to increase moisture in the incubators. 
part of the hatch, the eggs may be cooled from fifteen to twenty 
minutes with very good results. The exact degree and process 
of cooling are more or less disputed points, experiments proving 
that environment varies so much that no positive rule can be laid 
down. Itis evident that the eggs are considerably cooled during 
turning, and that the machine also cools off somewhat while the 
eggs are being taken out and replaced. Stop the cooling at the 
same time that the turning is stopped, or about the eighteenth or 
nineteenth day. 
Ventilation is essential in order that the gas liberated by the 
embryo may be discarded. The problem is, how to supply fresh 
