d. The egg, as laid, normally has no air cell. It forms as the egg cools, usually in
the large end of the egg, and develops between the shell membranes. The air cell is
formed as a result of the different rates of contraction between the shell and its
An average chicken egg weighs about 57 grams or 2 ounces. It is a very good
source of high-quality protein and of certain minerals and vitamins. The protein,
vitamin, and mineral contents of the albumen and yolk are described below.
(1) The protein of egg is complete; it contains all of the indispensable amino
(2) The thick white is made up mainly of the proteins: ovomucin,
ovoalbumen, conalbumen, ovoglobulin, and ovomucoid. Ovomucin gives structure to
the thick white.
(3) The albumen contains some water-soluble B vitamins, especially
riboflavin. The latter gives the greenish tint to the white.
(4) The thin white is composed mostly of proteins of the same kind as
contained in the thick white with the exception of ovomucin.
(1) The important yolk proteins are ovovitellin (about three- fourths of the
yolk protein) and livetin.
(2) The fatty substances of the yolk are mostly glycerides (true fat), lecithin,
(3) Yolk pigments (mostly xanthophyll) come from green plants and yellow
corn that the birds eat.
(4) The yolk contains practically all of the known vitamins except vitamin C.
The vitelline membrane is mostly protein similar to that of the shell membranes and is
fairly permeable to water. The higher concentration of the solids of the yolk causes the
yolk to increase in size and grow flabby by the inflow of water from the white as the egg
(5) The yolk contains iron, phosphorus, sulphur, copper, potassium, sodium,
magnesium, calcium, chlorine, and manganese, all of which are essential elements.