COOLING MEANS STRONG CHICKS 255 



the eggs at the morning turning only, not in the evening, unless 

 the hatch is pretty well advanced and the weather is exceedingly 

 warm. On the eighteenth day the eggs are turned and cooled 

 for the last time, after which the machine is closed and not opened 

 until the hatch is off. 



This cooling process not only exposes the eggs to fresh air, but 

 it causes the contents of the eggs to contract, and thereby draw 

 through the pores of the shell a fresh supply of oxygen, without 

 which the embryo could not thrive. 



The above methods are really in imitation of the hen's ways. 

 For the first few days the sitter remains close to her nest, after 

 which she leaves it once or twice a day, sometimes staying away 

 for an hour or more. Cooling can be overdone, like anything 

 else. But in most cases I have found too little cooling rather than 

 too much, to be in practice. After all, there can be no set rules 

 for an operation of this kind. The rules must be flexible, and 

 governed largely by the operator's judgment. For example, 

 in addition to weather conditions and the temperature of the 

 cellar, the amount of cooling should be regulated according to 

 the temperature of the machine for the past twenty-four hours. 

 If the temperature has been low, little or no cooling is advisable; 

 if the temperature has been high, then extra cooling is in order. 

 Moderation — common sense — that is the watchword in running 

 an incubator. Live up to the reason for a rule, rather than to 

 the letter of it. 



