DIGITALIS. In pharmacy, the leaves of the foxglove (q.v.) gathered from wild plants when about two-thirds of their flowers are expanded.
Digitalis contains four important glucosides, of which three are cardiac stimulants. The most powerful is digitoxin C3.HM01,, an extremely poisonous and cumulative drug, insoluble in water. Digitalin, is crystalline and is also insoluble in water. Digitalein is amorphous but readily soluble in water. It can there fore be administered subcutaneously, in doses of about one-hun dredth of a grain. Digitonin, on the other hand, is a cardiac de pressant, and has been found to be identical with saponin, the chief constituent of senega root.
Taken by the mouth digitalis is apt to cause digestive disturb ance, varying in different cases and sometimes severe. 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 is upon the un striped muscle of the arteries and arterioles.
The clinical influence of digitalis upon the heart is well defined. After a moderate dose the pulse is 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 pro longed, and since this is the period not only of cardiac rest but also of cardiac "f eeding"—the coronary vessels being compressed and occluded during systole—the result is greatly to benefit the nu trition of the cardiac muscle. So definite is this that, despite a great increase in the force of the contractions and despite experi mental 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 rested, its improved vigour being really due to its obtaining a larger supply of the nutrient blood. Almost equally striking is the fact that digitalis causes an irregular pulse to be come regular. Added to the greater force of cardiac contraction is a permanent tonic contraction of the organ, so that its internal capacity is reduced. The bearing of this fact on cases of cardiac dilatation is evident. In larger doses a remarkable sequel to these actions may be observed. The cardiac contractions become irregu lar, the ventricle assumes curious shapes—"hour-glass," etc.— becomes pale and bloodless, and finally the heart stops in a state of contraction and passes into rigor-mortis. Before this final change the heart may be started again by the application of a soluble potassium salt, or by raising the fluid pressure within it. Clinically the drug is cumulative, being very slowly excreted, so that after it has been taken for some time the pulse may become irregular, the blood-pressure low, and the cardiac pulsations rapid and feeble. These symptoms with gastrointestinal irritation and decrease in the quantity of urine passed indicate digitalis poison ing. It is by way of stimulation of the cardiac terminals of the vagus nerves that the heart's action is slowed. Thereafter follows the most important effect of the drug, which is a direct stimula tion of the cardiac muscle. This can be proved to occur in a heart so embryonic that no nerves can be recognized in it, and in por tions of cardiac muscle that contain neither nerve-cells nor nerve fibres.
The action of this drug on the kidney is of importance only second to its action on the circulation. In small or moderate doses it is a powerful diuretic. It seems probable that this is due to a rise in the general blood-pressure associated with a relatively dilated condition of the renal vessels. In' large doses, the renal vessels also are constricted and the amount of urine falls. In large doses it causes cerebral symptoms, such as seeing all ob jects blue, and various other disturbances of the special senses. It also lowers the reflex excitability of the spinal cord.
Digitalis is indicated when the heart shows itself unequal to the work it has to perform. This formula includes the vast ma jority of cardiac cases.