epends largely
upon the mode of life and upon the diet. Active muscular work,
especially out of doors, uses up the store of glycogen with great
rapidity; while rest and a sedentary life promotes its storage. The
body readily converts its supply of glycogen into glucose, the form in
which the body uses the carbohydrates for fuel.

~Cellulose~ is a woody, fibrous material insoluble in water and to a
certain extent impervious to the action of the digestive enzymes. This
carbohydrate constitutes the skeleton of plants just as the bones
constitute that of the animal body. It is probable that owing to the
length of time required for this carbohydrate to be broken down in
digestion, much of it escapes oxidation entirely. Hence, it passes
down the digestive tract lending bulk to the food mass and thus
promoting peristalsis throughout the whole of the digestive tract.

~Organic Acids.~--Certain of the carbohydrate foods (fruits and green
vegetables) contain appreciable amounts of organic acids or their
salts; oranges and lemons, for example, are rich in citric acid;
grapes contain considerable quantities of potassium acid tartrate,
apples and other fruits have malic acid; many of the fruits have
succinic acid; a few foods contain oxalic acid, or oxalates. All of
these organic acids are burned in the body to produce energy, with the
possible exception of the oxalates, which seem to have little, if any,
food value. According to Sherman, these organic acids have a lower
fuel value, per gram, than carbohydrates, but are reckoned as such in
computing a food in which they exist. The function of these acids is
chiefly that of neutralizing the acids formed in the body in
metabolism. Being base-forming in character, they function after
absorption and oxidation in the body as potential bases--the base
associated with the acid in their ash combining with carbonic acid to
form carbonates, which act as above described.

~Bacterial Action upon Carbohydrates of Foods.~--The bacteria that act
chiefly upon the carbohydrates belong to the fermentative type. The
substances formed as a result of this activity are certain
acids--lactic, butyric, formic, acetic, oxalic, and possibly alcohol.
Certain forms of carbohydrates are more susceptible to bacterial
fermentation than others. Herter claims that sucrose and glucose are
much more so than lactose, maltose, or starch. The substances thus
formed through bacterial activity are not believed to be to