Specimens are primarily preserved using fluids like alcohol or formaldehyde.
To comprehensively preserve natural history specimens, various methods are employed, each suited to the specimen type and research goals. Fluid preservation, the most common technique, involves immersing specimens in solutions that prevent decay. Here’s a breakdown:
Fluid Preservation
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Alcohol: Ethyl alcohol (ethanol), typically diluted to 70% with water, is widely used. It effectively dehydrates tissues, preventing bacterial growth. Denatured alcohol is often used to avoid consumption.
- Pros: Relatively safe to handle compared to formaldehyde; preserves DNA better than formaldehyde.
- Cons: Can cause tissues to shrink and harden over time; flammable.
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Formaldehyde: Commonly used as a 10% solution (formalin). It cross-links proteins, fixing tissues and preventing decomposition.
- Pros: Preserves tissue structure well; relatively inexpensive.
- Cons: Hazardous; can damage DNA over time; requires careful handling and disposal.
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Other Preservatives:
- Glycerol: Used to keep tissues pliable, often added after formaldehyde fixation.
- Propylene Glycol: A less toxic alternative to ethylene glycol (antifreeze), sometimes used for long-term storage.
Dry Preservation
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Drying: Suitable for plants, insects, and some animal specimens. Specimens are air-dried or desiccated using chemicals like silica gel.
- Pros: Simple and cost-effective.
- Cons: Can lead to shrinkage and distortion; susceptible to insect damage.
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Taxidermy: Used for preserving vertebrate animals, involving removing the internal organs, treating the skin, and stuffing it with materials to maintain its shape.
Freezing
- Ultra-low Temperature Freezing: Preserves tissues and DNA in pristine condition, often used for genetic studies. Specimens are stored in liquid nitrogen (-196°C) or ultra-low freezers (-80°C).
- Pros: Excellent for preserving DNA and other biomolecules.
- Cons: Requires specialized equipment and high energy consumption.
Mounting
- Insect Pinning: Used for insect specimens; insects are pinned through the thorax and labeled with collection data.
- Herbarium Sheets: Plant specimens are pressed, dried, and mounted on archival paper.
- Skeletal Articulation: Bones are cleaned, treated, and reassembled into a skeletal display.
Clearing and Staining
- Clearing: Tissues are made transparent using chemicals, allowing for visualization of internal structures.
- Staining: Dyes are used to highlight specific tissues or cells.
Embedding
- Resin Embedding: Tissues are embedded in resin blocks for sectioning and microscopic examination.
Key Considerations for All Preservation Methods:
- Proper Fixation: Ensures tissues are stabilized before preservation.
- Data Collection: Accurate collection data (location, date, collector) is crucial for specimen value.
- Labeling: Clear and permanent labels are essential for identification.
- Storage Conditions: Proper storage (temperature, humidity, light) is vital for long-term preservation.
The selection of a preservation method depends on the specimen, its intended use, and available resources. Combining methods can provide optimal long-term preservation for valuable natural history specimens.
