THE INCUBATION OF HENS' EGGS 225 



the case of a two-tray incul)ator tlie trays may he tTiriied end 

 for end one time and sliifted frfim side to side the next. 



While turning the eggs the inenl)at<>r (h)or should he eloscfl 

 to conserve hoth the temperature and nioistiire. All drafts 

 or any means of sudden chilling must he a^'oidelI. Tiu-ning 

 should he discontinued after the eighteenth day. 



Ventilating. — Different styles of incnl)ators vary so in 

 their styles of ventilation that it is difficult to make any 

 general suggestions that will apply in all cases. It is usually 

 well to follow the manufacturer's instructions. If, however, 

 poor results that cannot he ascrihed to any other cause 

 are had, means for admitting more air should he devised. 

 Few if any incuhators are overventilated. 



While the hatch is coming oft', ventilation should be 

 restricted for the purpose of conserving the moisture left 

 in the machine after the removal of the sand trays. As 

 soon as the hatch is over the ventilators should be opened 

 fully. 



Testing. — It is customary to test the eggs at the end of the 

 first week in order that all eggs that are not developing may 

 he removed. This is desirable in order to avoid breaking 

 eggs having dead germs in turning,, and that the developing 

 eggs may have the added room. In the case of poor fertility 

 the eggs from two or more machines may be combined. 

 White-shelled eggs may be tested as early as the third day, 

 with ^•ery dark-shelled ones the germ often cannot he seen 

 until the eighth or ninth day. 



The two classes of eggs tested out are "infertiles" and 

 "dead germs." Technically the term "infertile" refers to 

 the fact that an egg has never been fertilized, while practically 

 it includes those which have started to develop hut have died 

 before progressing far enough to be distinguished before the 

 tester. The dead germ refers to one that is fertile in which 

 the germ has died after developing far enough to be seen 

 before the tester. 



The so-called infertile egg appears to be clear save for a 

 floating shadow, which is easily distinguished as the yolk. 



The live germ is spider-like in appearance, the body of the 

 embryo representing the body of the spider and the radiating 

 15 



