Fixation

Fixation in microscopy is a crucial step in preparing tissue samples for examination under the microscope. The purpose of fixation is to maintain tissue structure, stop enzymatic activity, and prevent degradation of cell organelles and proteins. Fixation ensures that the tissue architecture and the relationship between different cellular components are preserved.

There are different methods and fixation devices that can be used, depending on the type of tissue and the intended examination. Some commonly used fixatives are:

1. Formaldehyde: Formaldehyde, in the form of a solution such as formalin, is a commonly used fixative. It reacts with proteins in the tissue and forms covalent bonds to maintain structure.
2. Glutaraldehyde: Glutaraldehyde is a fixative primarily used for electron microscopy. It provides better preservation of cell organelles and ultrastructures.
3. Bouin's solution: Bouin's solution is a fixative used for specific tissues such as embryonic tissues. It contains a combination of formaldehyde, acetic acid and picric acid.
4. Ethanol: Ethanol is often used for dehydration and fixation of thin cytological smears. It preserves cell structures and prevents cell shrinkage.

The fixation process usually involves the following steps:

1. Sample preparation: The tissue sample is carefully collected and placed in the desired cut or sliced to shape, depending on the intended study.
2. Fixant addition: The tissue sample is immersed in the fixative, usually in a liquid form such as a fixative solution. The specimen must be completely covered with the fixative.
3. Fixation time: The specimen is left in the fixative for a period of time, usually ranging from several minutes to several hours, depending on the tissue type and the fixative.
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5. Rinsing: After fixation, the tissue sample is thoroughly rinsed to remove excess fixative. This is usually done with a suitable rinsing agent, such as a buffer solution.

After fixation, the tissue sample can be processed for further analysis, such as embedding in paraffin or resin, cutting thin sections with a microtome and staining for microscopic observation.

Fixation is a critical step to maintain tissue integrity and obtain accurate results on microscopic examination. It ensures that the tissue structures are preserved and that the desired components are properly visualized under the microscope.