The thesis of Morgagni that diseases reside in certain organs of the human body has dominated pathologic anatomy and clinical investigation for centuries. Every diagnostic endeavor was directed toward establishing the fundamental organ disease. No doubt, this working hypothesis has been the cornerstone on which rests the edifice of modern medicine. The great advance of medicine throughout the nineteenth century is essentially founded on the method of correlating observations made in the hospital ward with those at the postmortem table. This clinicopathologic concept was further advanced by the recognition of an interdependence and unity of certain organs to form organ or tissue systems. Diseases of the hemopoietic or of the reticuloendothelial system represent such an extension of the scope of organ pathology. Nevertheless, one cannot justly maintain that an essential site is established in every disease. A number of acute infections and intoxications do not produce characteristic or even significant