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The Magnificant Egg (pt 1)

© Robert Hole, Jr.

Recently, a member of my household has been having some dental problems. Because of this, we've been having a lot of soft foods around the house, one of those foods being chicken eggs. I like eggs, but don't normally have them nearly as frequently as we've been eating them recently. Using, cracking, preparing and eating a fairly large number of them recently has gotten me thinking more about them, and how truly wonderous they are.

The egg is formed inside the female bird. Initially it consists of a single cell (and remains a single cell unless fertilized), which comprises the yolk (or ovum). The yolk is surrounded by several membranes and layers of albumin (the "white") and a shell.

The yolk is (usually) yellowish and contained by a thin membrane. In a fertilized egg, the yolk is a reservoir of nourishment needed for the developing bird chick. The albumin (white) primarily acts as a cushion for the developing embryo, allowing the yolk to float somewhat freely within the egg when it is turned in the nest. It also slows dehydration of the egg.

If fertilized, the embryo begins to grow from one side of the yolk. This side is called the "animal pole" of the yolk. The opposite end of the yolk is the "vegetable pole." The yolk is tied to the inside of the shell by chalaza (a part of the albumin) at each end of the yolk. This pair of twisted cords holds the yolk so that the animal pole is always upward. The chalaza can sometimes be seen as twisted white strands in freshly cracked egg.

If you take an uncooked egg from your refrigerator and gently roll it along your countertop, you'll find that it wobbles as it rolls. That's in part because the chalaza are trying to keep the yolk positioned in a certain way within the egg. This acts as a gyroscope and changes the course of the rolling egg.

Two thin layers of keratin (the same material in feathers and fingernails) surround the albumin of the egg. At the blunt end of the egg these two layers are separate to create an air pocket. This open area acts as a gas exchanger for the developing embryo.

The shell of the egg is primarily made of calcium carbonate, and is very porous. A chicken's egg shell may contain 17,000 pores over its surface. These pores permit oxygen to enter the egg, and carbon dioxide to leave it. If the pores are blocked, the developing chick will suffocate. The pores also allow some water to pass through the shell which, at least in part, helps maintain the proper temperature.

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