Due to their transparent nature, the cellular and intracellular structures in tissue samples cannot be microscopically examined until they are colored by dyes. Dyes are combined with other dyes and/or additional chemicals to make up stains. "Biological stains" refers to dyes/dye complexes that are used to stain tissue samples for microscopic analysis in the histology laboratory.
Biological stains exist as:
- General tissue stains - Uses one to three dyes to differentiate the nucleus from cytoplasm of cells, such as with hematoxylin and eosin (H&E).
- Special stains - involves multiple dyes in combination physically or sequentially by staining procedure to demonstrate specific structures within cells and tissue sections, such as connective tissue elements, that are often not demonstrated by the H&E.