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 to demonstrate specific structures within cells and tissue sections , such as connective tissue elements, that are often not demonstrated by the H&E.