Alcoholic solutions and absolute alcohol are ideal reagents for histology and cytology, storage and transport of samples. They are often used for sample preparation, during dehydration and rehydration of histological and cytological samples.

The samples are dehydrated before being included in paraffin. It is then a question of replacing the water contained in the sample by the inclusion medium. Since paraffin is not miscible with water, the fixed parts must be dehydrated in baths of increasing degrees of alcohol then in xylene and finally in paraffin heated to its melting point (+ 1 or 2 °). C). The interest of dehydration is to eliminate the fixer. The alcohol (ethanol) is then replaced by a paraffin-miscible solvent: it is either xylene or toluene (hydrocarbons). These substances eliminate ethanol. The duration of the dehydration cycle depends on the nature of the samples and their size.

A second dehydration step may be performed after staining and / or marking the tissue sections to apply a mounting medium for observation of the sample.