Digitalis, a genus of Scrophulariaceæ, natives chiefly of the south of Europe and temperate parts of Asia. One only, the Common Foxglove (q.v.), (D. purpurea), is a native of Britain. Other species have been introduced, notably D. lutea and grandiflora, with yellow flowers. The botanical name Digitalis (late Lat. digitale, 'the finger of a glove') refers, like the popular English name, to the form of the flowers.
The leaves of the Digitalis purpurea, collected before the expansion of the flowers and dried, are largely used in medicine, either in the form of powder, or as tincture or infusion. Digitalin granules, containing minute quantities of a mixture of the active principles, are also employed. The leaves owe their activity to the presence of certain bodies, which have been named digitalin, digitalein, digitoxin, and digitonin, the three first mentioned having the characteristic digitalis action, while the fourth is entirely different, and closely resembles saponin in its effects. The leaves and their preparations have a bitter taste. When given in large doses by the mouth, they produce violent vomiting and purging; this may prevent their absorption into the blood, but if absorbed, they may cause death by paralysing the heart's action. When the leaves are administered in medicinal doses, a peculiar action is exerted on the muscular substance of the heart and blood-vessels, causing the former to beat more slowly, regularly, and powerfully, and contracting the latter. By this combined action the blood-pressure is raised, and if dropsy be present, a diuretic action is exerted. Digitalis is also used in many organic forms of heart-disease, in nervous and functional irregularity of the heart's action, in cardiac weakness from long-continued disease, in œdema of the lungs, internal hemorrhages, and other conditions. When taken for a long time it may cause nausea and other digestive disturbances, and in a very few cases sudden and serious symptoms of poisoning come on. This constitutes the so called cumulative action of digitalis. In therapeutic doses digitalis should slow the pulse; if too large doses be given, the pulse becomes rapid and irregular.