Although physicians had already interpreted pus within a bodily compartment as a systemic threat, pus from infected tooth roots often drained into the mouth and thereby was viewed as systemically inconsequential. Amid focal infection theory, it was concluded that that was often the case—while immune response prevented dissemination from the focus—but that immunity could fail to contain the infection, that dissemination from the focus could ensue, and that systemic disease, often neurological, could result. By 1930, excision of focal infections was considered a "rational form of therapy" undoubtedly resolving many cases of chronic diseases. Its inconsistent effectiveness was attributed to unrecognized foci—perhaps inside internal organs—that the clinicians had missed.