498 A STUDY OF FARM ANIMALS 



expression than cooling, because it expresses more concisely 

 the real value that accompanies cooling. It is the fresh 

 oxygen that the eggs draw in as they cool that has a strength- 

 ening effect upon the embryo. The usual period for airing 

 is from the fifth to the eighteenth day. The eggs should be 

 turned three times a day morning, noon, and afternoon. 

 They should be aired once a day, preferably at noon. The 

 length of the airing period will depend upon the develop- 

 ment of the embryo and the temperature of the room in 

 which the eggs are aired. It will vary from two to three 

 minutes for eggs five days incubated early in the season, to 

 forty-five minutes for eighteen-day eggs in the late spring or 

 early summer. Turning by hand is undoubtedly more nearly 

 perfect than any automatic egg turning device, and if done 

 once a day in addition to the other turnings there will be a 

 marked decrease in the number of crippled chicks. 



Care of incubator after the hatch. Remove all shells 

 and unhatched eggs at the end of the twenty-second day. 

 Chicks hatched after the twenty-second day will be too weak 

 to prove worth raising. 



The incubator should be thoroughly cleaned and dis- 

 infected after each hatch. Certain communicable diseases 

 may be transmitted to the chicks through the medium of 

 bits of egg shell and droppings, unless the trays are kept in 

 a sanitary condition. Remove the trays and all portable 

 parts from the interior of the machine. Scrub these as well 

 as the inside of the machine with hot soapy water. Then 

 drain and disinfect everything with a two per cent solution 

 of creolin or zenoleum. Replace the trays, close the door 

 of the incubator, light the lamp, and let the machine dry 

 out. The fumes from the disinfectant will penetrate to all 

 parts of the machine. If burlap is used on the nursery tray, 

 use a clean burlap for each hatch. 



Eggs for incubation should be from vigorous, well-mated 

 fowls, and not from what might be called mongrel stock. 



