Cardiac failure has long been recognized as a cause of death in diphtheria. It is the factors which produce this death and the mechanism of the process that have caused dispute and discussion. Cardiac failure has been attributed by the majority of observers to an injury to the myocardium itself or its conducting system, but others have thought that the disturbance was extracardiac, that is, in the peripheral vasomotor system. On account of the various conflicting theories, it may be well to review briefly some of the opinions held respecting this very important phenomenon, before presenting our own observations. Coghlan1believes that the diphtheria toxin acts directly on the heart muscle, resulting in certain degenerative changes, and that this is the cause of the circulatory failure. Farr2carries this conception further, expressing the view that the diphtheria toxin has a peculiar affinity for heart muscle, the extrinsic and intrinsic cardiac