Fixatives may be simple or compound:

•  Simple fixative consists of one substance (e.g. formalin).
•  Compound fixative has two or more substances (e.g. Bouin’s, Zenker’s).

Fixatives can also be divided into following 3 groups:

•  Microanatomical fixatives, which preserve the anatomy of the tissue.
•  Cytological fixatives, which may be cytoplasmic or nuclear and preserve respective intracellular constituents.
•  Histochemical fixatives, employed for demonstration of histochemical constituents and enzymes.

Commonly used fixatives are as under:

• Osmium tetraoxide 
• Alcohol (e.g. Carnoy’s fixative)
• Picric acid (e.g. Bouin’s fluid)
• Glutaraldehyde
• Formalin

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