Tissue processing is the technique by which fixed tissues are made suitable for embedding within a supportive medium such as paraffin, and consists of three sequential steps: dehydration, clearing, and infiltration.


As up to 60% of the human adult body is water, dehydration is a process to remove water and fixatives (preservatives) from tissue. The next step after dehydration is called “clearing” and consists of replacing the dehydration solution with a substance (usually alcohols) that will be miscible with the inclusion medium (paraffin). Finally the clearing agent is removed and replaced by completely permeating the tissue with paraffin wax, called infiltration. This will allow the tissue to harden in a wax block from which thin histological sections can be cut.

After processing ‘Embedding’ is the process in which the tissues or the specimens are enclosed in a mass of the embedding medium using a mould. Since the tissue blocks are very thin in thickness, they need a supporting medium in which the tissue blocks are embedded so they can be held in a clamp and cut on a microtome.

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