Many wonder how a chick can breathe from inside the egg. The answer is quite intuitive: the "secret" in fact lies in the shell, whose walls are covered with tiny pores that act as real air intakes. Through these micro-cracks the chick is able to take in the necessary oxygen and eliminate carbon dioxide.
The porosity of the eggs also explains their limited shelf life; just think that once the farmers used to dip them in water and lime, so as to close the pores and increase their shelf life.
Some faecal bacteria, such as some salmonella strains, can also penetrate through the porosity of the shell. To limit the phenomenon, the cuticle intervenes, a membrane that covers the outer shell of the egg allowing the passage of gases and preventing the loss of water, which is essential for the development of the embryo.
