304 FORMATION OF THE EGG AND CHICKEN 
tact, while the inner one is adherent to the outer. At the large 
end, however, they are separate, and form a small cavity or sac 
known as the air cell. This is filled with air which has been drawn 
into the egg owing to the evaporation of the liquids, the size of 
the air cell increasing as the age of the egg increases. If this cell 
is found in any place but the large end of the egg, it usually denotes 
that the egg has been kept for some time, and has not been turned; 
thus the liquids settle and force the air to the highest point. 
Albumin.—Next is seen the albumin or white of the egg. This 
is a translucent liquid without definite structure, and, in the fresh 
egg, free from smell and taste. The albumin is easily coagulated 
by heat, only about 140 degrees being required. It is soluble 
in water. Under chemical analysis albumin is rather complex, 
being composed of varying proportions of oxygen, hydrogen, sul- 
phur, phosphorus, and carbon. The albumin can be readily 
divided into three distinct layers: a thin outer coat, a thicker 
middle layer, and a very much thickened inner stratum. In the 
latter can be found the chalaze, which are thickened strings or 
cords of albumin, having an outer terminus in the outer layer of 
albumin, and an inner securely interwoven in and around the yolk; 
they run lengthwise of the egg, are twisted in opposite directions, 
and hold the yolk in place. In appearance they resemble twisted 
cords. The albumin has two distinct functions; the first is that 
of protection, by forming a thick layer of material around the 
germ, at the same time that it furnishes the material in which it 
floats, thus protecting it from shocks which otherwise might prove 
fatal. The second purpose is that it provides material which goes 
directly into the formation of tissue for the embryo. _ 
The Yolk.—The yolk or ovum may be called the most import- 
ant part of the egg, since it contains within its outer wall, or vitel- 
line membrane, the germ or embryo and also the nourishment of 
the growing embryo. The yolk is nearly round, and light yellow 
in color, the degree or intensity of color varying with the character 
of the feed. In composition the yolk is considerably richer than 
the albumin, especially in phosphate of lime, there being but a 
trace in the albumin. The yolk is composed of two distinct por- 
tions arranged in concentric rings or layers, one being light in 
color and not coagulable upon the addition of heat, the other 
darker yellow in color and easily coagulable at a high temperature. 
In the lighter portion of the yolk is a hollow or indentation, in the 
upper part of which, and next to the vitelline membrane, lies the 
