HT Microtomy & Sectioning Techniques 2 — Questions and Answers
Question 1: What is the most common cause of 'chatter' artifact in paraffin sections?
- Dull microtome knife (Correct answer)
- Tissue over-fixation
- Paraffin too soft for room temperature
- Excessive section thickness
Correct answer: Dull microtome knife
A dull or nicked knife blade is the most common cause of chatter, producing alternating thick and thin bands across the section.
Question 2: Which microtome type is most appropriate for cutting large, undecalcified bone specimens embedded in plastic (methacrylate)?
- Rotary microtome
- Sliding microtome (Correct answer)
- Cryostat
- Vibratome
Correct answer: Sliding microtome
The sliding microtome, with its heavy construction and long knife stroke, is best suited for hard specimens like undecalcified bone in plastic.
Question 3: When sectioning a ribbon of paraffin sections, the sections curl away from the knife. What adjustment should be made?
- Increase the clearance angle (Correct answer)
- Decrease the clearance angle
- Increase section thickness
- Cool the paraffin block
Correct answer: Increase the clearance angle
Increasing the clearance (back) angle of the knife reduces friction on the bevel side and helps the ribbon lie flat.
Question 4: At what temperature should a water bath typically be maintained for floating paraffin sections?
- 5–10°C below the paraffin melting point (Correct answer)
- At the paraffin melting point
- 10–15°C below the paraffin melting point
- Equal to the embedding oven temperature
Correct answer: 5–10°C below the paraffin melting point
The floatation water bath is kept 5–10°C below the paraffin's melting point to allow wrinkles to relax without melting the section.
Question 5: A histotechnician notices that sections consistently compress along the cutting axis. Which action best corrects this?
- Hone and strop the knife (Correct answer)
- Warm the block face with a warm finger briefly
- Lower the water bath temperature
- Increase the tilt angle of the knife
Correct answer: Hone and strop the knife
Compression is most often caused by a dull knife; honing and stropping restores the cutting edge and reduces tissue compression.
Question 6: Which of the following knife profiles is preferred for cutting most routine paraffin-embedded tissues on a rotary microtome?
- Wedge (D) profile
- Plano-concave (C) profile (Correct answer)
- Biconcave (B) profile
- Tool-edge (E) profile
Correct answer: Plano-concave (C) profile
The plano-concave (C profile) knife, with one flat and one concave face, is the standard choice for routine paraffin sectioning on rotary microtomes.
Question 7: What effect does decreasing section thickness below the manufacturer's recommended minimum have on ribbon formation?
- Sections become too thin to form a continuous ribbon (Correct answer)
- Ribbon curves toward the flat side of the knife
- Sections wrinkle excessively on the water bath
- Paraffin melts prematurely during cutting
Correct answer: Sections become too thin to form a continuous ribbon
Sections cut below the reliable minimum thickness tend to fragment, preventing the formation of a continuous ribbon.
HT Microtomy & Sectioning Techniques 2
What is the most common cause of 'chatter' artifact in paraffin sections?