Non-proteolytic mutants were isolated from the Vollum strain of B. anthracis following ultraviolet treatment. The mutants were virulent for rabbits and mice and their non-proteolytic character was stable in culture and on serial passage in rabbits. The mutants produced protective antigen under suitable conditions of cultivation in vitro, and allowed longer incubation of the cultures without destruction of the protective antigen than did the parent strain. The meaning of the results is discussed.

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Several years ago in this laboratory an unusual type of agglutination was encountered in an investigation of the serology of Shigella alkalescens. On occasions a certain strain of S. alkalescens in homologous antiserum after 18 hours at 55 C showed the usual type of 0 agglutination with heavy compact granules on the bottom of the tube and crystal-clear supernatant fluid. The granules were altered only slightly when the tubes were shaken vigorously. On other occasions, however, this same strain in the same antiserum and under the same conditions of incubation gave an entirely different type of agglutination. The supernatant fluids were somewhat turbid and a soft mass of adherent cells lay on the bottom of the tubes. When the tubes were flirted gently, threads of