The practice of William Withering,1who published the first detailed study of digitalis about 150 years ago, is a matter not only of historical interest but of great practical importance to one dealing with the subject of digitalis dosage. At first glance it may appear as a stroke of genius that a fundamental law regarding the dosage of digitalis was stated at a time when practically nothing was known about the drug, not even that its beneficial effects were related to an action on the circulation. On the other hand, it may be the very fact that there were no distractions in the form of theories of cumulation and excretion or formulas of dosage that made it possible to keep the object clearly in view and to arrive at sound and practical principles. Physicians who profess to use a recommended plan of digitalis dosage frequently find their patients suffering