ble in water. _Digitalein_
is amorphous but readily soluble in water. It can therefore be
administered subcutaneously, in doses of about one-hundredth of a grain.
_Digitonin_, on the other hand, is a cardiac depressant, and has been
found to be identical with saponin, the chief constituent of senega
root. There are numerous preparations, patent and pharmacopeial, their
composition being extremely varied, so that, unless one has reason to be
certain of any particular preparation, it is almost better to use only
the dried leaves themselves in the form of a powder (dose 1/2-2 grains).
The pharmacopeial tincture may be given in doses of five to fifteen
minims, and the infusion has the unusually small dose of two to four
drachms--the dose of other infusions being an ounce or more. The
tincture contains a fair proportion of both digitalin and digitoxin.

Digitalis leaves have no definite external action. Taken by the mouth,
the drug is apt to cause considerable digestive disturbance, varying in
different cases and sometimes so severe as to cause serious difficulty.
This action is probably due to the digitonin, which is thus a
constituent in every way undesirable. The all-important property of the
drug is its action on the circulation. Its first action on any of the
body-tissues is upon unstriped muscle, so that the first consequence of
its absorption is a contraction of the arteries and arterioles. No other
known drug has an equally marked action in contracting the arterioles.
As the vaso-motor centre in the medulla oblongata is also stimulated, as
well as the contractions of the heart, there is thus trebly caused a
very great rise in the blood-pressure.

The clinical influence of digitalis upon the heart is very well defined.
After the taking of a moderate dose the pulse is markedly slowed. This
is due to a very definite influence upon the different portions of the
cardiac cycle. The systole is not altered in length, but the diastole is
very much prolonged, and since this is the period not only of cardiac
rest but also of cardiac "feeding"--the coronary vessels being
compressed and occluded during systole--the result is greatly to benefit
the nutrition of the cardiac muscle. So definite is this that, despite a
great increase in the force of the contractions and despite experimental
proof that the heart does more work in a given time under the influence
of digitalis, the organ subsequently displays all the signs of having
re