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 chalazae, 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 j^olk; 

 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 



