At microtomy, formalin fixed and paraffin embedded kidney sections are soft and mushy. This is most likely due to:

• A. Inadequate dehydration and clearing
• B. Over-dehydration
• C. Inadequate fixation
• D. Over-embedding

Answer: (A)

When tissue is not properly dehydrated and cleared before embedding, water and alcohol remnants remain and the tissue cannot be infiltrated evenly by paraffin. Dehydration removes water; clearing replaces the alcohol with a solvent miscible with paraffin. If either step is inadequate, paraffin infiltration is incomplete, producing a soft, gummy, or mushy block that yields soft sections during microtomy. Kidney tissue is especially sensitive to this because its delicate structures rely on good infiltration to maintain rigidity during cutting.

Over-dehydration tends to make tissue brittle and difficult to section, not soft and mushy. Inadequate fixation can smear or distort morphology but does not typically cause the tissue to be soft and mushy in the embedded block. Over-embedding would make the block excessively hard, not soft, and also disrupts section quality.