128 HATCHING AND REARING 



them into the tray; this permits the air cell to assume its 

 normal position. 



Turning. In artificial incubation we attempt to imitate 

 nature. The hen on the nest turns the eggs frequently by 

 means of her feet, beak, and body; in the incubator, the 

 attendant must do this with his hands. A good rule is to 

 begin on the third day of incubation to turn the eggs and to 

 turn them twice a day, morning and night, until the first 

 signs of pipping are noticed, which will usually be on the 

 twentieth day. The object of turning is to change the posi- 

 tion of the embryo, so that it will not adhere to the shell and 

 die. The growing embryo also needs oxygen, and turning 

 helps to keep the air cell in its proper position. The best 

 way to turn the eggs is to remove about one-tenth of those 

 in the tray and roll the others about in the tray by means 

 of the palms of the hands. It is unnecessary to turn each 

 egg half way over. 



Cooling. The hen occasionally leaves the nest, and thus 

 permits the eggs to cool ; so in artificial incubation, especially 

 in warm weather, we must artificially cool the eggs, not only 

 to lower the temperature, but to supply them with pure, 

 fresh air. A good rule for cooling is as follows : Do not cool 

 for any longer time than is required for turning, if the tem- 

 perature of the room is lower than 50 degrees Fahrenheit. 

 During the first week cool merely during the operation of 

 turning; in the second and third weeks gradually increase 

 the length of time for cooling until just before hatching 

 when the eggs can often be cooled for from a half hour to an 

 hour each day with advantage. Good hatches have been 

 known to take place when the eggs had been left out all 

 night, but this is risky. 



Testing the Eggs. The eggs should be tested on the 

 seventh and fourteenth days. Testing is a process which 

 informs the operator of the progress of the hatch, and the 

 condition of the hatching eggs, and also gives him an oppor- 



