Decalcifying Tissue for Histological Processing

The removal of calcium deposits is essential for good embedding procedure. Decalcification is usually carried out between the fixation and processing steps. Bone must obviously be processed in this way, but other tissues may also contain calcified areas. A variety of agents or techniques have been developed to decalcify tissues, each with advantages and disadvantages.…

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Working Safely with Fixatives

Fixatives are among the most hazardous substances used in life science research. Work with these substances under the hood wearing gloves, lab coat and safety goggles. Formaldehyde is a suspect cancer hazard and a strong sensitizer. It is harmful if inhaled or absorbed through the skin. High exposures may be fatal. Formaldehyde can cause blindness…

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Factors Affecting Fixation

Fixation protocols are usually straightforward. The tissue is cut to dimensions suited to the rate of penetration of the particular fixative and placed in the fixative solution. The number of factors affecting the fixation process includes buffering, penetration, volume, temperature and concentration. In fixation pH is critical. This is especially the case with formaldehyde, where…

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Non-Aldehyde Fixatives

Mercury Based Fixatives   Mercurials contain mercuric chloride. Their method of tissue fixation is poorly understood. While not penetrating tissue well and causing some tissue hardness, mercurials are fast and provide excellent nuclear detail. They are commonly used to fix hematopoietic and reticuloendothelial tissues. Alcohol Fixatives   Alcohols, including methyl alcohol (methanol) and ethyl alcohol…

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Aldehyde Fixatives

Formaldehyde and glutaraldehyde are the most commonly used aldehyde fixatives. They work by forming cross-links both within and between proteins, particularly between lysine residues. Damage to the tertiary structure of the proteins occurs on a limited basis. Formalin (37% aqueous formaldehyde) is normally diluted 10 fold and neutrally buffered to make a working fixative solution…

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Overview of Fixation

To maintain the tissue in as lifelike a state as possible, tissue for analysis is usually placed directly into a fixative solution upon removal from the body. Fixation is normally carried out as soon as possible to prevent autolysis and to reduce possible infectivity. Several factors determine the choice of fixative for a given application.…

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