26 
THE POULTRY BOOK. 
that causes the cracked sound that is given out on moving together the eggs 
in a nest when they -are nearly hatched. 
Inside the shell is the membrane or skin. This, which is formed of delicate 
interlaced fibres, appears single, hut is in reality double. The two skins separate at 
the larger end of the egg, forming an air-chamber, the size of which is a very good 
criterion of the freshness of the egg. When first laid, this air-chamber is not 
larger in extent than a threepenny piece ; but as the egg is kept the moisture 
evaporates through the pores of the shell, and as the fiuids diminish, air necessarily 
enters to supply their place ; hence the air-chamber gets larger and larger, so that 
on breaking the large end of a stale egg we sometimes see a cavity that seems to 
occupy a quarter of the shell. In the dispute between the Big-endians and the 
Little-endians, immortalized by Swift, the Big-endians most certainly had the best 
of the argument, for by opening the egg at the large end we can see its degree of 
freshness, an advantage which could not be claimed for the method advocated by 
the Little-endians. 
Inside the skin or membrane is the substance known as the white of the egg ; 
this is a thick glairy liquid, forming, usually, more than half of the entire weight. 
Most persons imagine that the white is uniform throughout, but in reality it pos- 
sesses a peculiar structure, being arranged in layers like those constituting the coats 
of an onion ; these layers, which are firmer and more dense towards the centre, can 
be readily seen, and separated from one another in the white of a hard-boiled egg. 
The difficulty of mixing white of egg with water or other liquids depends on the 
existence of these layers, which must be broken down or ** beaten up ” before it can 
be dissolved. 
The white is formed of a peculiar animal substance, termed by chemists albumen, 
and water. This albumen possesses remarkable properties, rendering it of great 
value, not only in cookery, but in many of the chemical arts. It forms a very 
large proportion of many parts of the bodies of all living animals, and is eminently 
nutritious. Beaten up with water it dissolves, and hence it is termed soluble 
albumen, but when heated to a temperature of about 180 ° Fah., that is to say, 
thirty-two degrees below the boiling point, it alters its character, becomes opaque, 
white, solid, and is no longer soluble. Even a weak solution cannot be heated to 
the boiling point without the albumen it contains coagulating and forming flocks, 
which separate from the liquid in a solid form and rise to the surface as a scum. 
On the other hand, if the white of egg be dried at a moderate temperature, it 
forms a pale yellowish substance, remains unaltered in its properties, and can be 
dissolved in water again without change. 
The remaining portion of the egg is known as the yolk, or yelk. This consists 
of albumen and water, mingled with a very large proportion of yellow oil ; the 
whole being so intimately mixed as to be eminently digestible. The yolk, in fact, 
is designed by Nature to form the first food of the chick at the period of hatching, 
and is one of the most nutritive of all known articles of food. The yolk is en- 
closed in an exceedingly delicate membrane, which prevents its admixture with the 
