. INCUBATION 259 



turning is sufficient. After that, at one turning each day they are 

 kept out of the machine until cool to the touch, the time ordinarily 

 required being from ten to thirty minutes, according to the tempera- 

 ture of the room and the development of the embryos, which, as they 

 increase in size, retain the heat longer. In warm weather a much 

 longer time may be required. Cooling is discontinued at the same 

 time as turning. Cooling is sometimes done by simply leaving 

 the door of the egg chamber open, but that does not expose the 

 eggs uniformly to the air. 



Testing is done at any time from the third or fourth to the 

 seventh day, and again from the twelfth to the fourteenth day. 

 The object of testing as early as development will show is to 

 remove the infertile eggs, which, if taken out early, are salable for 

 culinary purposes. 1 At the later tests the eggs containing dead 

 germs are removed. 



A record of each hatch is usually kept by the incubator operator, 

 either on a card kept on the machine, or in a notebook. In this 

 record is noted the number and description of the eggs set, the 

 temperature of the egg chamber at regular intervals, the number 

 of infertile eggs and dead germs removed at the tests, and any 

 irregularities which might affect the hatch. This routine work is 

 all simple and essentially mechanical. 



Factors in artificial incubation. To correctly adjust ventilation 

 and moisture is the special task in incubator operation. This will 

 be found easy or difficult according to whether the operator has 

 so placed the machine that its ordinary adjustments suit, or, if it 

 is placed otherwise, has used good judgment in estimating in what 

 way and how much the conditions vary from conditions in which 

 the machine was designed to be operated, and in making the appro- 

 priate changes. 



Ventilation and moisture questions in incubation are very 

 closely related interdependent. It is claimed for some incu- 

 bators that they need no moisture, and for others that the ven- 

 tilation in them is automatic. Such claims hold only for the 

 average condition to which a machine is adjusted as it leaves the 



1 An infertile egg that has been incubated is stale (the staleness depending 

 on the period of incubation) but may be as good as the ordinary run of market 

 eggs in hot weather. 



