The leaves of the purple foxglove are the part of the plant chosen for medicinal uses. Dried and finely powdered, they are employed in veterinary practice. An infusion and a tincture are likewise made from them, and an active principle is obtained and known as digitalin.
A tonic effect upon the heart is claimed for digitalis, as it increases the force of its contractions while lessening their number. By stimulating the nerves which contract the blood-vessels a better tone is imparted to them, and the circulation is rendered more efficient. Strength is given to the feeble heart, and when irregular or intermittent, it is made to act in a steady and rhythmic manner. It is found to have a beneficial effect in horses for a short time, but its continued administration results in irritation of the stomach and inappetence. Poisonous doses act by causing spasm of the heart and consequent death from cardiac paralysis. Digitalis excites the kidneys to excrete a larger amount of urine than usual, and for this reason it is employed in the removal of dropsical swellings.
StrophanthllS is the plant from which the arrow poison is derived, and its action in large doses is to paralyse the heart and other involuntary muscles. It is more soluble and rapid in its action than digitalis, but its effects are not so enduring. Continued administration, however, is less often attended with gastric disturbances. There are some cases of valvular trouble for which digitalis is unsuited, but in which strophanthus may be used with advantage.