32 BlGGr.K POILTRV BOOK. 



the upper surface of a fertile, live egg. The tempera- 

 ture of an infertile egg, or of an egg containing a dead 

 enibr3'0 will be lower than that of a live egg lying ad- 

 jacent in the same tray. It is important, therefore, iu 

 testing the temperature to place the bullj upon alive egg. 



By the tenth day the animal heat that has been 

 stored in the living embryos in the process of incuba- 

 tion l)ccomcs quite a factor in the temperature of the 

 machine. If the operator is not experienced or the 

 machine cannot l)e trusted to regulate its own tem- 

 perature, the thermometer is apt, about this time, to 

 shoot up to no degrees and the whole incubator full 

 of eggs to be destroyed. From this period to the end 

 less artificial heat is required. In a warm room a 

 large machine containing several hundred eggs will 

 hold its heat for hours at a time without the applica- 

 tion of any external heat whatever. 



It is thought necessar}^ to give eggs in incubators 

 a daily airing, after the fashion of the hen. This is 

 less essential when the hatching is done in a cold 

 room. In airing eggs it is best to remove them from 

 the machine in the trays and immediately close the 

 doors so as not to lower the inside temperature. 



While the eggs are being aired they should also 

 be turned. Nearly all machines have devices for doing 

 this, a trayful at a time, or automatically, by a clock- 

 work contrivance, l)ut in small machines it may be 

 done b}' hand and the relative position of the eggs in 

 the travs changed so as to l)cttcr insure an equal 

 chance for all. After the nineteenth day they should 

 not be handled, except as the shells are chipped the 

 broken side should be turned up. 



