Tiny holes

Eggshells aren’t completely solid and contain as many as 7,000 to 17,000 tiny holes — 1⁄1000 of an inch across — which allow for the input and output of oxygen, carbon dioxide and moisture. This is critical for a chick’s health and development. Gases are exchanged from the embryo to the shell via the allantois (a fetal membrane) and a network of blood vessels. You can see this egg science in action by candling one. A small amount of oxygen is stored inside the egg, in the air sac, or cell, which increases in size during the chick’s development. Prior to hatching, the chick breaks through the air sac to obtain its first “real” breath of air. That boost of oxygen enables the job of pecking free! (The air sac exists in a minimized form even in unfertilized eggs. It’s the “flat” area at the wide end of a hard-boiled egg.) At first, it might seem that the pores would provide a means for bacteria to invade. But the shell’s cuticle, or bloom — a final coating that goes over the eggshell — provides a protective seal. For nonfertilized eggs bound for the supermarket in the U.S., eggs are washed after collecting. But this washing removes the cuticle — a major reason eggs in U.S. stores must be refrigerated. Some other countries choose to opt out of the egg bath, the cuticle is left intact and refrigeration is not necessarily required. Eggs intended to hatch chicks should never be washed. The chick needs the protection of the cuticle. — Daniel Johnson Read more www.hobbyfarms.com/7-science-facts-chicken-egg.