Why do tissues require fixation?

The objective of fixation is to prevent autolysis and degradation of tissue and tissue components so that they can be preserved in their original life-like state with minimum alteration. Tissues that are not fixed do not process well. In the absence of fixation or even if fixation is delayed, tissue specimens can be irreversibly damaged, resulting in poor quality staining and tissue distortion. Regardless of the care taken subsequently in processing and staining the specimen, if it is not fixed, the morphological and histochemical information obtainable from the tissue will be compromised. Tissue fixation preserves the specimen in its original life-like state. This allows researchers to cut the specimen into sections thin enough to be translucent and to study tissue and tissue components more closely after sectioning.