ucose which
does ferment. There are several different modifications, or forms, of
dextrins, depending upon the extent to which the simplification of the
starch molecule by hydrolysis is carried. Three fairly definite forms are
generally recognized, as follows: _amylo-dextrin_, or soluble starch,
slightly soluble in cold water, readily so in hot water, giving a blue
color with iodine; _erythro-dextrin_ easily soluble in water, neutral
taste, red color with iodine; and _achroo-dextrin_, easily soluble in
water, sweetish taste, no color with iodine.

Commercial dextrin, which is much used in the preparation of mucilages and
adhesive pastes, is prepared by heating dry starch to about 250 deg. C. It
is composed chiefly of achroo-dextrin, mixed with varying quantities of
erythro-dextrin and glucose.

=Glycogen=, or "animal starch," is one of the most widely distributed
reserve foods of the animal body; in fact, it is the only known form of
carbohydrate-reserve in animal tissues. But it is present only rarely in
plants. It occurs in certain fungi, particularly in yeasts. In the animal
body, glycogen is found in all growing cells; also in the muscles and
blood; but most largely in the liver, where it is stored in large
quantities. The glycogen found in yeasts is identical with that found in
animal tissues. The quantity of glycogen in a yeast cell increases rapidly
as the yeast grows during the fermentation process.

Glycogen is a white, amorphous compound, readily soluble in hot water,
forming an opalescent solution similar in appearance to the solutions of
soluble starch. It is strongly dextrorotatory (specific rotatory power
+190 deg.), is colored brown by iodine, and is hydrolyzed to dextrin and
maltose, and finally to glucose.

=Lichenin=, =para dextran=, and =para isodextran= are dextrosans which have
been isolated from various lower plants. They all yield glucose when
completely hydrolyzed. They resemble starch in chemical properties, but
differ from it in physical form, etc.

(B) LEVULOSANS

=Inulin= replaces starch as the reserve food carbohydrate in a considerable
number of natural orders of plants, particularly in the Compositae. It is
the carbohydrate of the tubers of the dahlia and artichoke and of the
fleshy roots of chicory. It is often found associated with starch in
monocotyledonous plants, such as many species of _Iris_, _Hyacinthus_, and
_Muscari_. Among the monocotyledons