Physicians use bloodletting today to manage a few rare disorders. But on the basis of different physiological views about the body, many, not all, earlier “schools” or “systems” of western medicine used it frequently, some promiscuously, up to about the mid 1800s, when sharp expressions of skepticism markedly increased. Usage then diminished but did not disappear. From today's perspective, bloodletting would seem to have had little clinical value, indeed often been dangerous, e.g. notoriously, in treatment of the dying George Washington. Why then did widespread use of this therapy last as long as it did? A specific query arises with regard to influence of the work of P.C.A. Louis (1787-1872) and his published reports (1828, 1835). Historians cite the “father of clinical epidemiology” as the first to undertake analytical investigation, to find no evidence for any benefit of bloodletting, and imply his work had great influence on usage. But Louis claimed his results did show bloodletting shortened the course of lobar pneumonia and endorsed strongly its use for “inflammations which are severe and are seated in an important organ.” And those on either side of the issue later in the 1800s cited his work in support of opposite views. I suggest, rather than Louis' work, that the emergence of new views of the physiology of the body, the pathology of disease states, especially those termed “inflammations”, and perceived inadequate “rational” reconciliation of these with therapeutic practices such as bloodletting, accounted for the end of the widespread use of the procedure.