Cool But Never Cold
Cooling the eggs is of course practiced on The Corning Egg Farm. For the first week, five or six minutes will usually be found a sufficient time, but as the embryo grows the length of time should be increased.
It is quite impossible to give any exact length of period for cooling, and it must be determined by the feel of the egg to the hand. They should never reach a point where they can be termed perfectly cold, but should feel slightly warm as the palm of the hand is laid upon them. In cooling, the egg tray should be placed on top of an incubator or table so that the bottom is completely protected, otherwise the eggs will cool too rapidly. In other words they should lie as they do in the nest of the hen. According to atmospheric conditions, cooling, during the latter part of incubation, will sometimes reach from forty to sixty minutes. It is a practice with us to give the eggs a very long period of cooling on the 18th day, before they are placed in the incubator for the last time.
After closing the incubator on the 18th day it is not opened again until the chicks are removed on the 22d day.
To open the door and reach in to assist some chick out of difficulty means allowing the moisture to escape, and, while the one individual which was seen to be in trouble might be rescued, by the lack of moisture in the egg chamber, many others would be held fast in the shell.