Histotechnology I- Miscellaneous
Question No. 4. The Answer is: (B) Marchi's impregnation.
Discussion: Marchi's impregnation is based on selective blockage of osmium staining of normal myelin by treatment with an oxidizing agent. The Swank-Davenport modification uses potassium chorate as the oxidizing agent and appears to be perhaps the most reliable method. Marchi's impregnation asks for en bloc impregnation with osmium tetraoxide before sectioning. Degenerating myelin will stain black.
All others but Gallocyanun stain are myelin stains. Klüver-Barrera stain is a combined stain of Luxol fast blue for myelin and cresyl violet for neurons. Weil's method and Pal-Weigert method are also myelin stains. All these stains would give myelin a blue to dark-blue stain. Gallocyanin-alum method can be used to demonstrate nucleic acid and will give the Nissl substance a blue color. Non of these stains contain osmium.