Fixation is a crucial step in preparing specimens for microscopic examination.Its objective is to prevent decay and preserve cells and tissues in a "life-like" state. It does this by stopping enzyme activity, killing microorganisms and hardening the specimen while maintaining sufficient of the molecular structure to enable appropriate stainning methods to be applied (including those antigen-antibody reactions and those depending on preserving DNA and RNA). The sooner fixation is initiated following separation of a specimen from its blood supply the better the result will be. the most popular fixing agent is formaldehyde, usually in the form of a phosphate-buffered solution (often referred to as "formalin").