Abstract
Summary Purified Vi antigens isolated from P. ballerup, E. coli and S. typhosa, strains Ty2 and 61 were studied by means of the agar diffusion precipitin technique and found to be serologically identical. When high relative concentrations of Vi antigen were allowed to react with either homologous or heterologous antibody the zone of precipitate often splits into two lines. It was suggested that this phenomenon might be due to the presence of partially degraded antigen in the preparation tested. In contrast to acetone-killed bacilli, Vi antigens isolated from them were very poor immunizing agents. Mouse protection tests were used to indicate effectiveness of Vi antigens as immunizing agents. Tests on two strains of mice were compared. The Vi antigens studied were nontoxic for rabbits and ineffective in preparing the rabbits for the local Shwartzman reaction.
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