What is Paraffin Wax?
Paraffin wax is a white or colorless soft solid derived from petroleum, coal, or shale oil. It is commonly used in histology as an embedding medium for preparing tissue sections for microscopic examination. This medium is chosen for its ability to infiltrate tissues and provide support during sectioning.
Why is Paraffin Wax Used in Histology?
Paraffin wax is widely used in histology due to its several advantageous properties:
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Infiltration: It penetrates tissues effectively, ensuring that all cells and structures are supported.
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Sectioning: It hardens sufficiently to allow thin sections to be cut using a microtome.
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Preservation: It preserves tissue morphology and cellular details for subsequent staining and analysis.
How is Paraffin Wax Prepared for Embedding?
Before embedding, the paraffin wax must be melted and maintained at a temperature of approximately 60°C. The process involves several steps:
1.
Fixation: Tissues are fixed in a fixative like formalin to preserve cellular structure.
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Dehydration: Tissues are dehydrated using graded alcohols to remove water.
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Clearing: Alcohol is replaced with a clearing agent, usually xylene, to make tissues transparent.
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Infiltration: Tissues are infiltrated with melted paraffin wax, replacing the clearing agent.
What are the Steps in Paraffin Embedding?
The paraffin embedding process includes:
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Molding: Tissues are placed into molds and filled with molten paraffin wax.
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Orientation: Proper orientation of tissues is crucial for optimal sectioning.
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Cooling: The paraffin blocks are rapidly cooled to solidify the wax.
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Trimming: Excess wax is trimmed to expose the tissue surface.
What are the Limitations of Paraffin Wax?
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Shrinkage and Hardness: Can cause tissue shrinkage and may become too hard if over-cooled.
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Incompatibility with Some Stains: Certain stains and techniques may not work well with paraffin-embedded tissues.
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Artifacts: May introduce processing artifacts.
How Are Paraffin Sections Prepared?
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Sectioning: Thin sections (typically 4-10 µm) are cut using a microtome.
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Mounting: Sections are mounted on glass slides.
3.
Deparaffinization: Paraffin is removed from sections by treating with xylene.
4.
Rehydration: Sections are rehydrated through a series of graded alcohols.
What Are Common Stains Used with Paraffin Sections?
Common staining techniques include:
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Hematoxylin and Eosin (H&E): The most widely used stain for general tissue morphology.
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Periodic Acid-Schiff (PAS): Useful for detecting polysaccharides and mucosubstances.
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Immunohistochemistry (IHC): Allows for the detection of specific proteins using antibodies.
Conclusion
Paraffin wax plays a crucial role in histology, enabling detailed examination of tissue morphology and cellular structures. Its ability to infiltrate, support, and preserve tissues makes it an indispensable tool in the field. Despite some limitations, the benefits of using paraffin wax for embedding and sectioning far outweigh the drawbacks, making it a staple in histological laboratories worldwide.
