A satisfactory solution of the problem concerning the effect of giving digitalis, especially on the volume output of the heart, but of other problems concerning its action, is still outstanding. Difficulties in the way of complete understanding depend, it seems, on the circumstances in which digitalis is administered. Among these are the species of animal which is studied and the state of the heart, whether healthy or diseased. The value of digitalis as a therapeutic agent, being on many accounts a constant source of concern, is viewed as being involved in these issues. Discussion is often confused, action of the drug and the beneficence of that action being regarded as the same things. This inference need not necessarily be correct. The pulse rate may be lowered, the blood pressure raised, the excretion of water unchanged, the volume output of blood from the heart either decreased or increased; the effect of not one of these actions can supply a clue, a priori, to whether giving this agent is advisable.