framework of support for the dough, the heat is lessened or withdrawn,
the air will escape, or contract to its former volume, allowing the
distended glutinous cell walls to collapse; in either case the bread
will be heavy.

If carbonic acid gas, generated within the dough by means of
fermentation or by the use of chemical substances, be the means used to
lighten the mass, the gluten by virtue of its tenacity holds the bubbles
of gas as they are generated, and prevents the large and small ones from
uniting, or from rising to the surface, as they seek to do, being
lighter than the dough. Being thus caught where they are generated, and
the proper conditions supplied to expand them, they swell or raise the
dough, which is then termed a loaf. (This word "loaf" is from the
Anglo-Saxon _hlifian_, to raise or lift up.) The structure is rendered
permanent by the application of heat in baking.

BREAD MADE LIGHT BY FERMENTATION.

For general use, the most convenient form of bread is usually considered
to be that made from wheat flour, raised or made light by some method of
fermentation, although in point of nutritive value and healthfulness, it
does not equal light, unfermented, or aerated bread made without the aid
of chemicals.

THE PROCESS OF FERMENTATION.--Fermentation is a process of
decomposition, and hence more or less destructive to the substances
subjected to its influence. When animal and vegetable substances
containing large amounts of nitrogenous elements are in a moist state
and exposed to air, they very soon undergo a change, the result of which
is decomposition or decay. This is occasioned by the action of germs,
which feed upon nitrogenous substances, as do the various species of
fungi. Meat, eggs, milk, and other foods rich in nitrogenous elements
can be preserved but a short time if exposed to the atmosphere. The
carbonaceous elements are different in this respect. When pure starch,
sugar, or fat is exposed to the air in a moistened state, they exhibit
the very little tendency to change or decay. Yet if placed in contact
with decomposing substances containing nitrogen, they soon begin to
change, and are themselves decomposed and destroyed. This communication
of the condition of change from one class of substances to another, is
termed fermentation. If a fermenting substance be added to a watery
solution containing sugar, the sugar will be changed or decomposed, and
two new substances, alcohol and carbonic