In the preceding study, the acid-precipitating substance (A-P substance) of B. megateriun precipitatedneither with homologous antiserum nor with heterologous antiserum and that of B. anthracis did notprecipitate with heterologous antiserum. As one of the reason, the lower concentrations of these A-Psubstances in test solutions were considered. In this study, therefore, the A-P substances were prepared inlarge amounts and relatively concentrated solutions of these A-P substances were used. As was expected, the A-P substance from each organism exhibited not only the specific antigenicity but also the commonantigenicity. However, the titers against homologous antiserum were higher than those against heterologousantiserum. The tests performed in agar gel exhibited the presence of considerable amounts of specific antigenin the A-P substance of each organism. These results suggest that the specific antigen components containedin the culture fluid can be concentrated by acid-precipitation.
Antigenicity of the A-P substance of each organism was hardly influenced by heat (100°C, 20 min.) orby trypsin digestion. These results suggest that the A-P substance contains thermostable, nontrypsin-digestibleantigen components.