INCUBATION 65 



Air passes through the pores of the shell for use by the 

 embryo as it develops. If the pores are stopped by a coat of 

 oil or dirt, the embryo smothers. If the eggs are permitted 

 to dry out too uiuch, there will not be eiiougli albumen left 

 to make the chick large and strong enough to break the shell 

 and get out, and it will die in the shell. 



After about twenty-one days of incubation, the chick is 

 ready to leave its shell (Fig. 48). Although it is not very 

 strong, it is able to make its way through the hard shell with- 

 out very much difBculty, for Xature has provided it with a 

 hard, sharp point which is fastened to the end of its beak. 

 With the aid of this little instrument, the chick breaks out 

 of its shell. It first makes a little hole in about the middle 

 of the largest part of the egg. Then it turns itself around 

 inside of the egg, breaking the shell as it goes. This makes 

 a broken ring around the egg, so that just a little pressure is 

 needed to force the two halves of the shell apart, and let 

 the little chick out into a big world where all things are 

 strange and new. 



The process of incubation goes on just the same 

 whether the eggs are hatched by a hen or by an incubator. 

 An incubator, as you know, is a machine whereby chickens 

 are hatched by artificial heat. As the demand for poultry 

 and poultry products became greater and greater, some 

 such machine became necessary; for men wanted to rear 

 greater numbers of chickens than it was possible to hatch 

 5 



