The five, or more, glucosides which are present in the leaves and seeds of
the foxglove (_Digitalis purpurea_) have been extensively studied, as they
are the active principles in the various digitalis extracts which are used
in medicine as a heart stimulant.

=Digitoxin=, C_{34}H_{54}O_{11}, which is the most active of these
glucosides in its physiological effects, when hydrolyzed, yields
digitoxigenin, C_{22}H_{32}O_{4}, and a sugar having the formula
C_{6}H_{12}O_{4}, which is known as "digitoxose" and is supposed to be a
dimethyl tetrose.

=Digitalin=, C_{35}H_{56}O_{14}, is also strongly active. When hydrolyzed,
it yields digitaligenin, C_{22}H_{10}O_{3}, glucose, and digitoxose.

=Digitonin=, C_{54}H_{92}O_{28}, constitutes about one-half of the total
glucosides in the extract which is obtained from most species of the
digitalis plants. It is much less active than the others. It is a saponin
(see page 90) in type. On hydrolysis, it yields 2 molecules of glucose, 2
of galactose, and one of digitogenin.

=Gitonin=, C_{49}H_{80}O_{23}, containing 3 molecules of galactose, one of
a pentose sugar, and one of gitogenin; and =gitalin=, C_{28}H_{48}O_{10},
containing digitoxose and gitaligenin, have also been isolated from
digitalis extracts.

The structural arrangement of the characteristic groups in these glucosides
has not yet been definitely worked out.

=Cymarin=, the active principle of Indian hemp (_Apocynum cannabinum_), is
similar in type to the digitalis glucosides. When hydrolyzed, it yields a
sugar known as "cymarose," C_{7}H_{14}O_{7}, which seems to be a monomethyl
derivative of digitoxose, and cymarigenin, C_{23}H_{30}O_{5}, a compound
which is either identical or isomeric with the organic residue obtained
from other members of this group.

THE SAPONINS

The saponins constitute a group of glucosides which are widely distributed
in plants, whose properties have been known since early Grecian times. They
have been found in over four hundred different species of plants, belonging
to more than forty different orders.

The most characteristic property of saponins is that they form colloidal
solutions in water which produce a soapy foam when agitated, and are
peculiarly toxic, especially to frogs and fishes. In dry form, they have a
very bitter, acrid taste, and their dust is very irritating to the mucous
membranes of the eye, nose, and throat.

On hydrolysis, the saponi