Explain Acidic Stains (anionic) - Types of Stains?

These are sodium, potassium, calcium or ammonium salts of coloured acids, which on ionization give negatively charged chromogen. These are best under acidic conditions. Most acidic dyes are unable to bind to the cell surface and also not able to penetrate into the cell because of repulsion by cell surface. These possess negatively charged groups, like, carboxyl (- COOH), phenolic, hydroxyl (-OH) so have a strong affinity to positively charged cell structure and macromolecules, like proteins. Example: Eosin, Picric Acid, Rose Bengal, Acid Fuchsin etc.