DIGITALIS, dij-i-taTis, a name given to the leaves of the plant Digitalis purpurea (see FOXGLOVE), of the second year's growth. This is a biennial herb which is largely cultivated for ornament. It is about two to five feet high, with large succulent leaves and tubular urn shaped purple flowers growing in a raceme. It is a native of southern and central Europe, and is extensively cultivated throughout the world, although the cultivated leaves are not as service able as those of the wild plant. The leaves, which lose on drying about 75 per cent in weight, are mostly obtained from the wild plants growing in the mountainous regions when two thirds of the flowers are expanded. The leaves should not be kept more than one year, as the quality deteriorates very rapidly. The active principles in the digitalis leaves consist of four or five glycocides: digitoxin, digitophyllin, dig italin, digitalein and cligitonin. The seeds also contain large amounts of active glycocides. The action of digitalis on the body is complex. It is primarily a local irritant causing secondary paralysis of the sensory nerve-endings. It is bitter to the taste, followed by burning and swelling of the mucous membrane. It is an irri tant to the intestines, where it may cause nausea and vomiting. After absorption the chief action of the drug is on the central nervous system, the heart and the blood vessels. The action on the nervous system is of secondary value to the heart activities, although there is distinct stimu lation throughout. The action of the drug on the heart-muscle is the most important property possessed by digitalis, both pharmacologically and therapeutically. Here, by reason of the complicated physiology of the heart action, the differing effects of digitalis on this organ are somewhat difficult to comprehend. Digitalis
stimulates primarily the muscular fibres of the heart. It stimulates the cardiac nervous gang lia; and it stimulates, and then paralyzes, the cardiac inhibitory nerve, the pneumogastric. Thus the normal heart, under the action of small doses of digitalis, is at first made to beat some what more strongly and rapidly; but as soon as its action upon the pneumogastric becomes mani fest, in larger and increasing doses, the heart action becomes more powerful and is somewhat slowed; and in full medicinal doses, frequently used in medicine when the effects of digitalis are desired, the action of the heart is much stronger and considerably slower. The blood-pressure is high, and the arteries are contracted. If, how ever, the use of digitalis is pushed beyond this point, its action as a paralyzant of the pneumo gastric begins to be evident. By reason of this loss of the inhibitory action of the pneumogas tric, the heart action at first is stronger, and the beat becomes more rapid. If still further toxic doses are given, the heart runs away, as it were. It beats very rapidly, irregularly, and with in creasingly weakened force, until it finally stops exhausted. Digitalis also increases the secre tion of urine; it raises the pressure of the blood vessels, and increases the amount of blood in all the organs of the body, including the heart itself. It is thus one of the great cardiac tonics, when used within physiological limits, and is indicated in most cases of heart disease where there is malnutrition caused by the dilatation of the chamber or a leakage of the valves.