370 ELEMENTS OF AGRICULTURE 



(3) The structure of a boiled egg. Crack the large end of a 

 hard-boiled egg carefully. Remove the shell, piece by piece, to avoid 

 tearing the shell membrane. 



(a) Observe the air-space and the two membranes, which are 

 separated with difficulty. Note that the outer membrane is the thicker 

 and tougher. 



(6) Cut the egg lengthwise through the middle. Observe the 

 lighter-colored, flask-shaped center of the yolk, and the darker yolk 

 arranged around it in concentric layers. Note the "germinal vesicle," 

 or "germinal disc," at the upper part of the light yolk. Observe that 

 the yolk is at one side and not in the center of the white of the egg. 

 Note also that the germinal disc is on the upper side of the yolk. This 

 is because the yolk is lighter in weight than the albumen, and hence 

 floats. The germinal disc on the surface of the white yolk is lighter 

 than the dark yolk. 



Snyder gives the chemical composition of the dry substance of the 



inside of the egg as: 



Protein Fat 



Albumen (white of the egg) 88.92 .53 



Yolk 20.62 64.43 



It will be seen that there is a large amount of fat in the yolk and 

 almost no fat in the albumen. Fat is lighter than albumen, hence rises 

 to the surface. This may be observed in practice by holding a fresh 



Pio. 194. Section of an egg 



egg in front of an egg-tester and noting the tendency of the yolk to 

 float upward. 



This tendency of the yolk to float to the surface makes it necessary 

 to turn eggs frequently when they are kept for hatching, otherwise the 



