Regarding action on heart and circula tion, it is deemed best to give in abstract the various views:— Wood sums up the action of the drug by saying that in moderate doses it stimu lates the muscular portion of the heart (probably of its ganglia), increases ac tivity of the inhibitory apparatus, and produces contraction of the arterioles. As a consequence of the first action, the cardiac beats become stronger; as a re sult of the last, there is narrowing of the blood-paths, and to the passage of the vital fluid an increased resistance which, acting on the already-excited inhibitory system, aids in slowing the pulse. De cided therapeutic doses produce great re duction and sometimes dicrotism of the pulse, and increase the size and force of the wave; at the same time the arterial tension is augmented.
Murrell states that tlie greatest and characteristic action of the drug is that it affects elasticity of cardiac muscle without at first modifying its contractile power, as indicated by increase in the volume of the pulse, although the abso lute working power of the heart is neither increased nor decreased; at the same time the quantity of blood driven into the aorta is greater than before, not only at every beat of the pulse, but even in a given unit of time; notwithstanding the number of pulsations be diminished, the result is a better filling of the arteries and an increase in blood-pressure. Ac companying this condition there is slow ing of the pulse due to stimulation of the inhibitory mechanism of the heart. Finally, in conjunction with continuous high pressure there is irregularity both in the action of the heart and in the fre quency of the pulse. Digitalis does not exert a sedative action on the muscular substance of the heart; and although the organ may be beating more slowly it may also be doing more work.
Ringer and Sainsbury teach that digi talis undoubtedly does affect directly— i.e., immediately—the muscular tissue of the heart, including persistent contrac tion. Inasmuch as this action on the heart is independent of the agency of nervous tissues, it seems presumable that it may affect other muscular tissue in the same way. It does undoubtedly cause strong contraction of the blood-vessels when these are quite cut off from the cen tral nervous control; hence it must act either directly on the muscular tissue of the wails of blood-vessels or on some pe ripheral nervous apparatus that governs the muscular tissue of the blood-vessels. In therapeutic use it may be conceived that digitalis will act in different ways: by strengthening the action of a weak heart; by reducing the strength of the beats of a heart acting too powerfully; by lessening the frequency of the heart's beats; by correcting irregular action of the organ; by increasing tonicity and so lessening the size of the cavities, thereby obviating the condition of over distension in which the stretched ven tricles are -unable to contract upon the contents, a condition threatening com plete asystole—the second of these prop ositions a different and fuller dosage will probably be required.
it has been the general view that each preparation is ca,pable of producing effects peculiar in some respects to itself. But the physiological effects of digi talein and digitoxin are identical with those of digitalin, except that they do not stimulate the vasomotor centre or the pneumogastric apparatus, and so do not directly raise blood-pressure or slow the heart. In other words, they increase the force of ventricular contraction. The effect of digitonin is to depress the vagus nerves, so it antagonizes the vagal effect of the digitalin and prevents digi talis from slowing the heart to the ex tent that would result from the use of digitalin alone. It also depresses the heart-muscle. H. A. Hare (Therap. Gaz., Aug. 16, '97).
Attention called to the vasomotor ac tion of digitalis; with a rather generous dose, migraine due to cerebral cong,estion can be overcome, where a small dose, acting on the circulatory centre, would simply aggravate the condition. Diuresis is produced only in those cases in which there is anasarca, and is due to aim sarca ; often there is diuresis without increase of blood-pressure. When the dropsy has disappeared thc diuresis ceases. Diminution of the dose indi cated on the disappearance of dropsy. Chief indications of digitalis are in creased frequency and irregularity of the pulse and the presence of cedema. In cases the ITVerSe of these it is useless or harmful. Warning is given against its careless use in myocarditis with fatty degeneration and in cardiac asthenia with dilatation. In cardiac dilatEttion of gathic origin digitalis is harmful, for it is not tolerated by the stomach. Ar teriosclerosis is not a, contra-indication if caution is used. Where increased fre quency of the pulse or dropsy are pres ent in aortic insufficiency, digitalis is distinctly indicated. The same is true in mitral stenosis. In mitral insuffi ciency it has its widest use, but it is late in the disease that digitalis is most needed. When tricuspid accompanies mitral insufficiency, the former, unless great care be taken, is made to disappear too rapidly by digitalis, and pulmonary apoplexy results, through increase of capillary pressure. Of the preparations, digitalin is preferable. M. Potani (Jour, de Med., '9S).