Handbook of histology methods for bone and cartilage

Fixation is the chemical or physical process that allows tissue sections to be viewed in a close approximation to the living tissue.1 Histological fixation practices have been derived from many other fields, such as the leather tanning industry. Fixation is the single most important factor in achieving a well-prepared section for microscopic analysis. Fixation processes should be standardized so that subtle changes in microanatomy may be detected by comparing similarly fixed sections. When tissue is removed from the host, a good fixative will stop autolysis (the dissolution of cells by intracellular enzymatic digestion) and putrefaction (the breakdown of tissue by bacterial action) by inactivating the enzymes, bacteria, and molds that begin to form immediately after death. It will also protect the tissue from excessive shrinkage and swelling, and it will not dissolve or distort the tissue. Dehydrating agents and clearing agents can cause distortion of tissue, so the chosen fixing agent will also protect the cellular constituents so that they will not be altered by these chemicals.2 The fixative must also protect the tissue during the embedding process, which involves polymer impregnation at a high temperature. Finally, it must protect the tissue during sectioning, where the potential for mechanical damage is high.