Definitions: Structural Stains (Endospore, Capsule, and Flagella)

Endospore: formed by several genera in the order of Bacillus and Clostridium which are the most familiar genera. Endospores are usually called "resting bodies" because they do not metabolize and are resistant to heating, various chemicals, and many harsh environmental conditions. Endospores are not for reproduction; they are formed when essential nutrients or water are not available.

Capsules: secreted chemicals that adhere to their surfaces forming a viscous coat, genetically determined, size of the capsule is influenced by the medium on which the bacterium is growing. Most capsules are formed of polysaccharides. Capsules have an important role in the virulence of some bacteria.

Flagella: most common means of motility; thin proteinaceous structures that originate in the cytoplasm and project our from the cell wall. They are very fragile and are not visible with a light microscope.