A serologically reactive polysaccharide of dextran nature was produced from sucrose by the action of some enzyme or similar heat-labile agent contained in sterile filtered extracts derived from sucrose broth cultures of Leuconostoc mesenteroides. Rigorous controls were included to prove that this reaction occurred in the absence of microorganisms.

Purified preparations of the dextran formed by the sterile extracts were similar to the dextran elaborated in sucrose broth cultures of the bacteria in respect to both chemical and serological properties. The serological likeness was established not only by tests against leuconostoc antiserums but also by cross reactions with antiserums of Types 2, 20, and 12 pneumococci and by tests against a series of variously absorbed antiserums.

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