Incubation E855 



with all types of incubators and under varying atmospheric condi- 

 tions. But the fact that eggs incubated by hens undergo more or less 

 cooling and yet hatch well, makes it appear essential that those artificially 

 incubated shall be treated correspondingly. Results prove this theory 

 io be true. 



It has been proved that excessive ventilation causes a too rapid 

 evaporation of the egg contents. Eggs cooled too much are affected 

 similarly. Therefore, for the first seven days of incubation it is best 

 not to leave them out of the incubator longer than is necessary for proper 

 turning. The length of time to cool eggs may be determined by touching 

 several of the eggs to the eyelid or to the lips. If the eggs are cooled suffi- 

 ciently, they will feel cool at the first touch. They should never be 

 left out of the incubator long enough to become cold. The expert operator 

 can tell when the eggs are cooled to the proper point by placing the palms 

 of the hands on the eggs. In this way he gets the average ^temperature 

 of several eggs. The loss of heat from all eggs is not the same in amount 

 during a given time. Eggs containing embryos of low vitality give up 

 their heat much more rapidly than do eggs containing embryos of high 

 vitality. Eggs should be cooled to the point at which they cease to 

 give off heat and are about to become cold. 



When cooling is begun, it will take only a very few minutes, perhaps 

 four or five, to cool the eggs sufhciently; the length of time depends on 

 the temperature of the room. The coohng should be gradually extended 

 over a longer period as the embryos grow. In warm weather thirty 

 to sixty minutes may be needed in order to air the eggs properly during 

 the latter stages of incubation. On very sultry days extra cooling is 

 beneficial; less is desirable on cool days. In cold weather only a com- 

 paratively short time will be required in order to cool the eggs sufhciently. 

 Cooling may be done after either the morning or the evening turning 

 of the eggs, or at both times. If the eggs are cooled twice each day, 

 a period of only half the length of time mentioned above should be re- 

 quired each time. 



Eggs may be cooled on a table, or perhaps on the top of the incubator. 

 Care shoiild be taken that no part of the tray containing the eggs shall 

 project over the edge of the table or the incubator, for the eggs on the 

 projecting part of the tray would be likely to become overcooled. Some 

 authorities advise cooling the eggs in the incubator by opening the doors. 

 This is not good practice. While the doors remain open the heat is con- 

 stantly escaping, and the incubator bcx^omes cooled as well as the eggs. 

 A longer time is then required in order to bring the temperature of the 

 egg chamber back to the proper degree than when the eggs are cooled 

 outside and the incubator kept closed. Cooling should be discontinued 

 on the nineteenth day of incubation. 



