In histology processing, what is the infiltration step?

• A. Infiltration is the process of dehydrating tissue.
• B. Infiltration is the process of saturating tissue with the embedding medium.
• C. Infiltration is the clearing of tissue with clearing agents.
• D. Infiltration is the fixation of tissue with fixatives.

Answer: (B)

The infiltration step means saturating the tissue with embedding medium (usually molten paraffin or resin) so the tissue is fully permeated and supported for embedding and sectioning. After dehydration removes water and clearing replaces it with a solvent compatible with the embedding medium, the tissue is exposed to the molten embedding medium. That medium infiltrates the tissue, filling spaces and surrounding structures so the specimen can be embedded and later cut into thin sections without distortion. If infiltration doesn’t occur well, sections can be brittle or crumble because the tissue isn’t properly supported. Dehydration removes water, clearing replaces alcohol with a clearing agent, and fixation preserves structure with fixatives—these are distinct steps from infiltration.