VENTILATION 341 



oxygen. The problem is, how to supply fresh air without too 

 great a loss of moisture from the egg, due to evaporation. Evap- 

 oration of the fluid in the egg is influenced by the rapidity with 

 which the air circulates through the egg chamber, and by the 

 humidity of the air itself; hence the factors of ventilation and 

 moisture are closely related. 



There are three methods of ventilating the smaller or individual 

 incubator. The first, and most efficient, is by the introduction of 

 fresh air into the machine, the intake being at the lamp box and 

 the pure air heated as it enters the machine. The second is by 

 the use of small ventilators controlled by sliding valves which lead 

 directly to the inside of the machine through the wall. The third 

 is ventilation through the bottom of the incubator, the bottom 

 being provided with openings or slits, and, in some cases, so con- 

 structed that it can be let down. In some machines these three 

 modes are combined, while in others only one or at the most two 

 are used. Whatever the system used, there should be an abundance 

 of fresh air passing slowly through the chamber, and this can be 

 regulated by muslin or burlap curtains to cut off any draft. 



Evaporation and Moisture. The real gauge of the ventilation 

 is the evaporation which takes place within the egg in a given 

 time; hence, one of the best means of ascertaining the exact rela- 

 tion between ventilation and moisture is a study of this evapora- 

 tion. It can be determined by testing or candling the eggs, and 

 noting the increased size of the air cell. For instance, when the 

 egg is first put into the machine the air cell is very small, being 

 only about one-eighth of an inch in depth. Under normal con- 

 ditions it will have increased on the third day to about one- 

 quarter of an inch in depth, on the eighth day to about three- 

 eighths, on the fifteenth day to about five-eighths, and on the 

 nineteenth day to about three-quarters. This is caused by air 

 penetrating the shell and taking the place formerly occupied by 

 the evaporated liquids. 



The evaporation which takes place in the normal egg during 

 incubation has beeji determined as follows: One hundred eggs 

 of average size will lose during the first five days of incubation 

 8.28 ounces, during the next seven days 12.05 ounces, and 

 during the next seven days 12.044 ounces. This shows the high 

 degree of loss, and the loss becomes still greater as the hatch 

 progresses. 



Many experiments have been conducted to determine the de- 



