SUMMARY: Toxic and non-toxic fractions, isolated from culture supernatant fluids or from organisms of O78 K 80, were examined with the electron microscope after negative staining with phosphotungstate. Preparations of endotoxin from the supernatant fluids (‘free endotoxin’) contained large numbers of rod-like particles, considered to be the native undegraded endotoxic lipopolysaccharide-protein complex. Phenol-water extraction of either free endotoxin particles or whole organisms caused aggregation of the complex, leading to chain-like structures. Both ‘rods’ and ‘chains’ were observed in an endotoxin preparation extracted from organisms by aqueous ether. A non-toxic predominantly polysaccharidic preparation from was not visible after negative staining; but this fraction, and to a lesser extent the toxic fractions derived from culture supernatant fluids, were found to contain well-defined fragments believed to be derived from the bacterial cell wall.


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