A Contribution to the Problem of the Virulence (“VI”) Antigen of B. typhosus

Abstract

1. The strains of B. typhosus, which are inagglutinable, or non-sensitive to somatic O agglutinins, are virulent, whereas the agglutinable, or sensitive strains, show a low virulence.2. Virulence and inagglutinability of strains seem to depend upon the presence in them of a virulence (Vi) antigen.3. A considerable protective action, observed by means of active and passive immunisation, is exerted by the inagglutinable strain used (205 D), because it contains Vi antigen.4. When the O and H agglutinins are eliminated through absorption, the agglutination reaction may serve to demonstrate in vitro the presence of the Vi antibody.