composition. As is well known, an egg consists of a porous shell lined
with a fine, but tough, membrane that encloses the white and the yolk
and serves to protect them. The yolk is divided from the white by a
delicate membrane, which permits it to be separated from the white when
an egg is carefully broken. This membrane extends to each end of the
shell in the form of a small cord, and it is so fastened to the shell as
to hold the yolk evenly suspended. The porous nature of an egg shell is
required to give air to the developing chick, but it is this
characteristic that permits eggs to spoil as they grow old and are
exposed to air, for through these minute pores, or openings, the water
in the egg evaporates and air and bacteria enter. Of course, as the
water evaporates and is replaced by air, the egg becomes lighter.
Because of this fact, the freshness of eggs can be determined by placing
them in water. When they are fresh, they will sink in cold water, but as
they decompose they become lighter and will float.

Since it is known that the spoiling of eggs is due to the entrance of
air through the porous shell, it may be inferred that their decay may be
prevented either by protecting the shell so that air cannot enter or by
keeping the eggs at so low a temperature that bacteria cannot grow.
Although stored eggs always deteriorate more or less, both of these
methods of preservation have proved very satisfactory, the former being
used largely in the home and the latter finding its solution in cold
storage. A knowledge of how eggs can be preserved, however, is of great
value, for if there were no means of preservation and eventual
marketing, the price of eggs would at times rise to actual
prohibitive limits.

3. That eggs as an article of food are growing in importance is
indicated by the fact that their production has come to be a large and