Antitoxic and antibacterial immunity have been clearly differentiated in the experimental mouse infection produced by the diffuse colonial variant of the Smith strain of Staphylococcus aureus.

Immunization with crude toxoid protected mice from otherwise lethal doses of alpha hemolysin, but did not alter mortality following intraperitoneal infection with living staphylococci. Conversely, animals immunized with heat killed vaccines were readily killed by culture supernates containing alpha hemolysin, but were strikingly protected from otherwise fatal intraperitoneal infection with viable staphylococci.

Protection was directly related to the ability of the immunizing substance to promote early intraperitoneal phagocytosis of the infecting inoculum. In these studies with the Smith diffuse variant, rapid intraperitoneal phagocytosis was induced by vaccination with whole cell bacterial vaccines but not by alpha hemolysin toxoid.

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