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Staining Technique Since many tissue constituients have the same optical densities, they must be stained for light microscopy. Staining for light microscopy is performed with mostly water-soluble stains. Therefore, the paraffin first is removed from the section, then the tissue is rehydrated and stained. Subsequent to staining, the section is again dehydrated so that the cover slip may be permanently affixed by the use of a suitable mounting medium. Although there are various types of stains that have been developed to visualize many components of the cells and tissue, they may be grouped into three classes; stains that differentiat between acidic and basic components of the cell; specialized stains that differentiate between the fibrous components of the extracellular matrix; and metallic salts that percipitate on tissue, forming metal deposits on them. The most commonly used stain in histology are hematoxylin and eosin, commonly reffered to as H & E. Hematoxylin is a base that preferentially colors acidic components of the cell a bluish tint. Because the most acidic components are DNA and RNA, the nucleus and regions of the cytoplasm stain dark blue. These components are referred to as Basophilic. Eosin is an acid that dyes the basic components of the cell a pinkish color. Because many cytoplasmic constituents have a basic pH, regions of the cytoplasm stain pink. These elements are said to be acidophilic. Many other stains are also utilized in preparing specimens for histological studies. taken from Gartner & Hiatt, "Color Text Book of Histology", W.B. Saunders COmpany, 1997, pge 2 |