Fixation is a crucial step in the preparation of histological sections. By terminating ongoing biochemical reactions, fixatives kill tissues and prevent post-mortem decay, enabling fresh biological tissues to be preserved in a state as close to natural as possible. Fixatives disable biomolecules, such as proteolytic enzymes that would normally digest and damage the sample. Also, through their toxicity and unpalatability to micro-organisms, fixatives protect the sample from external damage.
Irrespective of how carefully a fixative is applied, the process of fixation always alters the sample by introducing artifacts that interfere with the interpretation of the slide. Artifacts vary according to tissue type and processing technique, so when deciding on your exact methodology, be sure to take artifacts into account and select techniques that minimize their appearance.
A range of different fixatives are available, including the two most common: formaldehyde and glutaraldehyde.