Histological section

Histological section refers to thin slices of tissue applied to a microscopic slide, usually around 5 to 10 micrometres thick, which are viewed under a microscope. For further discussion of histological section and staining methods, one should review histology article.

Method for making histological sections

Gross cutting

The specimen is cut into the correct size and configuration prior to fixation and microtome cutting. The specimen is stained and positioned for proper orientation.

Fixation

Fixation is done either by the fixed tissue method with paraffin, or by frozen section. With fixed tissue method, the tissue specimen is preserve in either formaldehyde or an acidic solution until it is processed. The tissue is then removed from the preservative, dehydrated with multiple solvent baths, and fixed in hot liquid parafin. The hardened parafin block with the fixed tissue is then cut with the microtome. With frozen tissue sectioning, the tissue is immediately frozen prior to processing (frozen section).

Microtome Cutting

The frozen tissue block embedded in a frozen cutting medium, or the paraffin fixed tissue is cut using a very fine knife called a microtome. A cryostat is a micotome mounted inside a freezer for processing frozen tissue.

Mounting

The frozen thin slices of tissue are mounted on a warm glass slide at room temperature, or the paraffin embedded slides are mounted on a heated glass. This allow them to be stained and ready for staining.

Staining and coverslipping

Multiple stain baths are used to make the tissue more visible to the naked eye. Please see histology for discussion of the stains used. Sections usually have a very thin piece of glass applied over the surface called a cover slip.