260 POULTRY CULTURE 



factory. Even for approximately average conditions it is found 

 that if the instructions of the manufacturer indicate that moisture 

 is to be supplied in uniform quantity, they leave ventilation to be 

 regulated by the operator ; and if ventilation is to be constant, 

 moisture is to be regulated according to the judgment of the 

 operator. These things are generally implied, if not always 

 plainly expressed. Though the operator may overlook them at 

 first, experience soon shows him what he must do. 



The source of moisture in incubation. The eggs incubated furnish 

 the moisture in incubation. An egg is from 60 to 65 per cent 

 water and has a porous shell. Exposed to ordinary temperatures, 

 the contents of an egg gradually dries up through evaporation of its 

 water. The rate and amount of evaporation under incubation may 

 be found by weighing the eggs at intervals. Experiments to deter- 

 mine this point have been made at several experiment stations. In 

 nineteen days of incubation a fertile egg may lose by evaporation 

 as much as 1 7 per cent of its original weight ; the least loss re- 

 corded in an experiment is 1 1 per cent. On this (11 per cent) 

 basis a setting of eggs weighing 26 ounces would lose by evapora- 

 tion 2.86 ounces. It is estimated 1 that this amount of moisture, if 

 distributed evenly through nineteen days, would be sufficient to 

 saturate the air in a nest/<??/r times an hour throughout the entire 

 period. In other experiments the percentage of evaporation was 

 still higher. Atwood 2 estimates that "one .hundred fertile eggs of 

 average size will lose 234.9 grams, or 8.28 ounces, during the first 

 five days of incubation ; 341.8 grams, or 12.05 ounces, during the 

 next seven days; and 352.8 grams, or 12.44 ounces, during the 

 next seven days." 



Use of ventilation. The essential function of ventilation in arti- 

 ficial incubation is to remove the moisture and gases exhaled by 

 the eggs. In an improperly designed incubator, ventilation might 

 be necessary to carry off the fumes of the lamp entering the egg 

 chamber. In any incubator, ventilation must provide for the re- 

 moval of moisture to allow normal evaporation from the egg. As 

 the condition of the egg is affected by the condition of the egg 



. l Day, " Humidity in Relation to Incubation," Bulletin No. 163, Ontario Depart- 

 ment of Agriculture. 



2 Bulletin No. 73, West Virginia University Agricultural Experiment Station. 



