ETIOLOGY OF THE EPIDEMIC ACUTE RESPIRATORY INFECTIONS COMMONLY CALLED INFLUENZA

Epidemics of acute respiratory infections have occurred at irregular intervals for centuries in various parts of the world, and their prevention has been one of the most formidable problems in preventive medicine. These infections, different from other epidemic diseases, seem least liable to modification by hygienic or geographic conditions, and at some time in its history almost every race of people has suffered from their ravages. During these visitations, recorded in centuries of medical history, the general mortality is greatly increased; the etiologic agent, independent of its own virulence, may increase the death rate by combining with preexisting diseases, or by lowering the resisting power of the individual to such an extent that other more formidable infections gain a foothold and cannot be overcome. Furthermore, it is very striking that, notwithstanding the wide diversity of conditions under which these great epidemics have occurred, the clinical manifestations of the disease have