OSMIUM TETROXIDE AND THE MARCHI METHOD: REACTIONS WITH POLAR AND NON-POLAR LIPIDS,PROTEIN AND POLYSACCHARIDE

1. The reactions of tissues with OsO₄ and the Swank-Davenport KClO₃-OsO₄ (Marchi) reagent have been studied by blockade of the reducing groups of unsaturated lipid, protein and polysaccharide. Only blockade of the —CH=CH— bond prevented osmiophilia after brief staining (18 hr.).

2. Tissue-protein is neither stained nor demonstrably impregnated after brief treatment with OsO₄.

3. Chromatographic separation of degenerating myelin revealed that the Marchi-substance is eluted in the esterified cholesterol fraction.

4. Unsaturated lipid but not protein or polysaccharide are stained by brief treatment with OsO₄. The Marchi reaction distinguishes hydrophilic from hydrophobic unsaturated lipid.