Oxidisable carbohydrates may be complexed with lipids, as glycolipids. Some of these resist extraction in the usual reagents used for paraffin processing. They may be removed, or extracted, by treatment with relatively harsh lipid solvents, often at elevated temperatures.
Note: Lipid solvents are often very inflammable or explosive, and must be used with caution. Ideally, they should be used in an explosion safe fume hood, and there should be no open flames or source of electrical sparks in the vicinity.
Place dewaxed sections into the solvent in a well sealed container at ambient or elevated temperature for an appropriate period of time. Most lipids will be extracted by simple immersion at ambient temperatures for several hours.
Some lipids will resist extraction at ambient temperatures and may require elevated temperatures for several hours. Heat should be applied in an explosion safe oven or by an electrically heated sand bath. This should be done in an explosion safe fume hood.
Should it be necessary to use boiling solvents to extract a lipid, then a reflux condensor should be used in an explosion safe fume hood. Ensure the solvent container is properly vented so that any pressure from fumes is released, and that the condensing capacity is significantly greater than the fume production. An electrically heated sand bath is strongly recommended, and direct heat should never be applied. Do not use ether this way.
After extraction the solvent should be rinsed off with absolute ethanol, after which the section may be celloidinised if desired, before proceeding with the staining method.
Lillie, R.D., (1954)
Histopathologic technique and practical histochemistry Ed.2
Blakiston, New York, USA.