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Tissue Fixation

As defined by Freida Carson, a fixative alters tissue by stabilizing the proteins so that it is resistant to further changes. The main purpose of tissue preservation is to keep the cellular morphology intact through various processes to ensure that the specimen is diagnostic. As soon as the tissue is removed from the body, it begins breaking down through enzyme action. Fixatives prevent putrefaction (decay) and autolysis (enzyme attack). Autolyzed tissue components will not stain properly, hindering diagnosis. Time in fixative is dependent on the tissue size. Larger samples require more time in fixative, simply because there are more tissue layers for the fixative to penetrate. Fixation occurs from the outside of the tissue inward. Many times, under-processed tissue will be fixed on the surface, while the center remains soft and mushy. The fixative volume should be 15 to 20 times greater than tissue volume, in order to keep the fixative from becoming depleted and also to cover the sample completely.