Gelatin-Paraffin Wax

A useful technique on occasion is the use of gelatin encapsulation followed by paraffin wax processing. This enables small, fragmented tissues to be embedded together without loss, or the processing of exfoliated cells into a block for sectioning. Since gelatin is an animal protein it can be fixed with formalin and treated as a piece of tissue.

1. Prepare a 5% - 10% solution of gelatin in water. This may be made ahead of time and suitable volumes aliquoted into test tubes, sealed and refrigerated. Before using, examine carefully to ensure there is no contamination. If clean, melt at about 37°C just prior to use. Do not heat to much more than this temperature.
2. a. If processing fragmented tissues, filter through an appropriate filter bag or paper, and add the fragments to a suitable volume of gelatin. Mix, and allow to settle.
   b. If processing exfoliated cells, centrifuge the cell suspension gently to concentrate, decant the excess fluid and add sufficient gelatin to cover the cell button.
3. Allow the gelatin to solidify, refrigerated if necessary.
4. Immerse the gelatin block into 10% NBF overnight to fix the gelatin.
5. Process, using a paraffin wax schedule as usual.

The surface area of the impregnated block will depend partly on the size of the container used for solidifying the gelatin. However, gelatin absorbs water from a tissue flotation bath and may well expand, so should be picked up on a slide quickly after being sectioned. Experience will determine how large the gelatin button should be. Gelatin blocks may become harder and a little brittle with this technique. Sectioning is best done with a sharp knife, taking sections as thin as possible.

 

References
A common technique.

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