Sections from a well-processed colon block come off wrinkled and about 20% shorter than the block face in the direction of cutting. The blade has already cut 40 blocks, and the trimmed block has sat for 20 minutes in a 30 °C room. What is the best correction?

Chill the block face and use a fresh area of blade

Lower the flotation bath to room temperature

Re-process the block again from the dehydration stage

Cut thicker sections and skip the flotation bath

At the rotary microtome, paraffin sections come off one at a time instead of joining into a ribbon. A common cause is:

A flotation bath that is too hot

After an overnight processor run, blocks from every cassette are soft, with white crystalline patches in the wax, and tissue crumbles away from the wax at microtomy. Checks: last ethanol 99% by hydrometer; xylene clear, not milky; wax baths at 60 °C for 56 °C wax; the first wax bath smells strongly of xylene. What is the most likely cause?

Xylene carried over into the wax baths

Wax baths set too hot for the wax

Fixation too short before processing

Water left from incomplete dehydration

Histotechnology: processing, embedding and microtomy

54 Kerala MSc MLT Entrance practice questions on Histotechnology: processing, embedding and microtomy, part of Pathology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
Sections from a well-processed colon block come off wrinkled and about 20% shorter than the block face in the direction of cutting. The blade has already cut 40 blocks, and the trimmed block has sat for 20 minutes in a 30 °C room. What is the best correction?
1. AChill the block face and use a fresh area of blade
2. BLower the flotation bath to room temperature
3. CRe-process the block again from the dehydration stage
4. DCut thicker sections and skip the flotation bath
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Answer: A · Chill the block face and use a fresh area of blade
Compression shortens and wrinkles each section along the direction of cutting. Its main causes are a warm, soft block and a dull blade, and both are present here. Chilling the block on ice or a cold plate hardens the wax, a sharp blade cuts cleanly, and any slight compression left is removed as the section spreads on the warm flotation bath. The block is well processed, so reprocessing is not needed.
- B: A cold flotation bath stops the section from spreading out.
- C: The tissue is well processed; the fault lies in the cutting conditions.
- D: Thick sections hide detail, and flotation is what removes residual wrinkles.
Question 2 · Easy
The angle between the lower facet of the microtome knife and the face of the block is called the:
1. AWedge angle
2. BClearance angle
3. CBevel angle
4. DRake angle
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Answer: B · Clearance angle
The clearance angle is the small tilt that stops the lower facet of the knife from rubbing on the block face; it is usually only a few degrees. If it is too small, the facet presses on the block and sections come off unevenly. The bevel angle lies between the two cutting facets at the edge, and the wedge angle between the two sides of the knife. Disposable blade holders have the clearance angle set by the holder.
- A: The wedge angle is between the two sides of the knife.
- C: The bevel angle is between the two cutting facets at the edge.
- D: The rake angle involves the upper facet, over which the section slides.
Question 3 · Medium
At the rotary microtome, paraffin sections come off one at a time instead of joining into a ribbon. A common cause is:
1. AA flotation bath that is too hot
2. BWax too hard or block too cold
3. CA nick in the blade edge
4. DWater left in the tissue
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Answer: B · Wax too hard or block too cold
Sections join into a ribbon because the edges of each section soften slightly and stick to the next as it is cut. Very hard wax, an over-chilled block or a cold room prevents this. Warming the block face slightly, for example by breathing on it, or using a softer wax usually restores the ribbon. Blade nicks cause splits, and water left in the tissue causes crumbling.
- A: The flotation bath acts after cutting and cannot stop a ribbon forming.
- C: A nick in the blade causes a split in the section, not loss of the ribbon.
- D: Water from poor dehydration leaves soft, crumbling tissue.
Question 4 · Medium
A transiliac bone biopsy is sent to measure osteoid seams in suspected osteomalacia. It should be embedded, without decalcification, in:
1. ACelloidin
2. BMethyl methacrylate resin
3. CPolyethylene glycol
4. DParaffin wax
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Answer: B · Methyl methacrylate resin
Osteoid is unmineralised bone matrix, and osteomalacia is judged by the width and extent of osteoid seams against mineralised bone. Decalcification would remove the very difference being measured, so the biopsy is embedded undecalcified in hard methyl methacrylate resin and cut on a heavy-duty microtome. Stains such as von Kossa or Goldner's trichrome then separate mineralised bone from osteoid. Paraffin is too soft to support undecalcified bone.
- A: Celloidin is too soft for mineralised bone and very slow.
- C: Polyethylene glycol is far too soft to cut mineralised bone.
- D: Paraffin cannot support undecalcified bone for thin sections.
Question 5 · Hard
After an overnight processor run, blocks from every cassette are soft, with white crystalline patches in the wax, and tissue crumbles away from the wax at microtomy. Checks: last ethanol 99% by hydrometer; xylene clear, not milky; wax baths at 60 °C for 56 °C wax; the first wax bath smells strongly of xylene. What is the most likely cause?
1. AXylene carried over into the wax baths
2. BWax baths set too hot for the wax
3. CFixation too short before processing
4. DWater left from incomplete dehydration
Show answerHide answer
Answer: A · Xylene carried over into the wax baths
Clearing agent carried into the wax lowers its melting point and spoils its crystal structure, so blocks are soft and crystalline and the tissue is poorly supported. The strong smell of xylene in the first wax bath points to wax that has not been changed often enough. The 99% ethanol and clear xylene rule out water carry-over, which would turn the xylene milky, and the wax temperature is correct. Discarding the first wax and rotating fresh wax into the last bath corrects it.
- B: 60 °C is only 4 °C above the melting point, which is correct.
- C: Poor fixation gives soft tissue that stains poorly, not crystalline wax.
- D: Water would turn the xylene milky, and the ethanol reads 99%.
Question 6 · Easy
Which embedding medium is soluble in water, so that tissue can go into it without dehydration or clearing?
1. APolyethylene glycol (Carbowax)
2. BCelloidin (nitrocellulose)
3. CEpoxy resin (Araldite)
4. DEster wax
Answer and explanation in LearnFree account
Question 7 · Hard
During an operation, a surgeon sends a hard, gritty fragment of a bony tumour for intraoperative diagnosis. The tissue cannot be cut in the cryostat. What is the best way to give a rapid opinion?
1. ADecalcify it in 5% nitric acid, then freeze it
2. BFreeze it at -40 °C and cut with a new blade
3. CEmbed it in more OCT and cut sections at 20 µm
4. DMake touch imprints of the cut surface for rapid staining
Answer and explanation in LearnFree account
Question 8 · Medium
Leaving small biopsies in xylene for much longer than the schedule allows tends to make them:
1. AHard and brittle
2. BSwollen and pale
3. COpaque and milky
4. DSoft and mushy
Answer and explanation in LearnFree account
Question 9 · Hard
Graded alcohols for a processor are prepared from 95% ethanol (rectified spirit). What volume of 95% ethanol, made up to 500 mL with distilled water, gives 70% ethanol?
1. A368 mL
2. B350 mL
3. C132 mL
4. D475 mL
Answer and explanation in LearnFree account
Question 10 · Hard
Sections of a decalcified bone marrow trephine and of brain repeatedly float off plain glass slides during staining. They were picked up from a water bath with no adhesive and dried upright for 10 minutes at room temperature. Which change is most likely to prevent this?
1. AShorten the time in the alcohols before staining
2. BRaise the flotation bath to 10 °C above the wax melting point
3. CCut the sections at 10 µm instead of 4 µm
4. DUse adhesive-coated slides and dry them longer with heat
Answer and explanation in LearnFree account
Question 11 · Medium
Dioxane can replace both the alcohols and the clearing agent in paraffin processing because it:
1. AMakes tissue transparent when cleared
2. BDissolves fat faster than xylene does
3. CMixes with both water and molten paraffin
4. DFixes the tissue at the same time as it dehydrates it
Answer and explanation in LearnFree account
Question 12 · Medium
A fresh lymph node block in the cryostat at -32 °C gives sections that crack and shatter into fragments. What is the best adjustment?
1. ACoat the cut face with more OCT
2. BCool the block further to -40 °C
3. CCut faster with a firmer stroke
4. DWarm the block to about -18 °C
Answer and explanation in LearnFree account
Question 13 · Easy
In a cryostat, the anti-roll plate:
1. ACools the knife below the chamber temperature
2. BKeeps each section flat on the knife as it is cut
3. CSets the thickness of each section cut
4. DHolds the frozen block firmly on the chuck
Answer and explanation in LearnFree account
Question 14 · Medium
A histology laboratory without air conditioning finds in the Kerala summer that its blocks soften and the sections compress and crumple at the microtome. Which change to the embedding wax helps most?
1. AKeep the embedding wax above 70 °C
2. BUse a wax with a higher melting point
3. CAdd a little xylene to soften the embedding wax
4. DUse a wax with a lower melting point
Answer and explanation in LearnFree account
Question 15 · Medium
Large blocks, such as whole-brain slices or undecalcified bone in resin, are best cut on a:
1. ARocking microtome
2. BFreezing microtome
3. CBase sledge microtome
4. DRotary microtome
Answer and explanation in LearnFree account
Question 16 · Easy
A clearing agent extracted from citrus peel, used as a less toxic substitute for xylene, is:
1. ACedarwood oil
2. BChloroform
3. CToluene
4. DLimonene
Answer and explanation in LearnFree account
Question 17 · Hard
Biopsies loaded on Friday evening finished processing at 2 a.m. Saturday and stayed in heated wax at 60 °C until Monday. Their blocks are hard and brittle and the sections crack and chatter. Biopsies from weekdays, processed and embedded at once, cut well. What prevents a repeat?
1. ARaise the wax bath temperature to keep the wax fully fluid
2. BUse delayed start so tissue waits in fixative, not hot wax
3. CAdd an extra xylene change at the end of the schedule
4. DUse a lower melting point wax for weekend runs
Answer and explanation in LearnFree account
Question 18 · Medium
Commercial embedding waxes such as Paraplast contain added plastic polymers. Their main purpose is to make the wax:
1. AFiner-grained and more elastic, so it ribbons well
2. BMelt at about 40 °C, so heat damage is avoided
3. CWater-soluble, so tissue needs no dehydration
4. DStain-resistant, so the slide background stays clear
Answer and explanation in LearnFree account
Question 19 · Medium
Acetone dehydrates tissue within minutes, yet it is little used on routine processors. The main reason is that acetone:
1. AShrinks and hardens tissue and is highly flammable
2. BDissolves the paraffin wax in later baths
3. CCannot remove bound water from formalin-fixed tissue
4. DIs not miscible with xylene or other clearants
Answer and explanation in LearnFree account
Question 20 · Hard
On an ultramicrotome, a ribbon of epoxy sections floats on the trough, and each section shows a reflected interference colour. The sections are for routine transmission electron microscopy. Which colour shows the correct thickness?
1. AGrey
2. BPurple
3. CBlue
4. DSilver to pale gold
Answer and explanation in LearnFree account
Question 21 · Easy
Which clearing agent hardens tissue least and suits delicate tissues such as CNS, although it clears very slowly?
1. ACedarwood oil
2. BAbsolute ethanol
3. CChloroform
4. DXylene
Answer and explanation in LearnFree account
Question 22 · Medium
On a dry day in an air-conditioned room, paraffin ribbons cling to the blade holder and lift towards the operator's hands. Which simple measure helps most?
1. ACut thicker sections of about 10 µm
2. BIncrease the clearance angle to about 15 degrees
3. CRaise humidity near the microtome or use an antistatic device
4. DWarm the block surface on the flotation bath
Answer and explanation in LearnFree account
Question 23 · Medium
A renal biopsy is sent for direct immunofluorescence for immune-complex deposits. The core for this test should reach the laboratory:
1. AIn 10% neutral buffered formalin, for paraffin sections
2. BUnfixed, in saline or Michel's medium, for cryostat sections
3. CIn Bouin's fluid, for paraffin sections
4. DIn 2.5% glutaraldehyde, for resin embedding
Answer and explanation in LearnFree account
Question 24 · Hard
A renal biopsy is sectioned at 5 µm like routine surgical blocks. On H&E and PAS, the glomeruli look crowded with nuclei and the basement membranes cannot be assessed. The pathologist suspects the appearance is artefact. What should the laboratory do?
1. ARestain the same sections with PAS
2. BRe-embed the cores on their edge
3. CRecut the block at 8-10 µm
4. DRecut the block at 2-3 µm
Answer and explanation in LearnFree account
Question 25 · Medium
At embedding, the tissue is placed with the surface to be examined facing down on the floor of the mould. Why?
1. AWax cools fastest at the bottom and supports the tissue best there
2. BThe cassette label fixes the side from which the block is cut
3. CThe floor of the mould becomes the face of the block that is cut first
4. DAir bubbles collect at the top of the mould and spoil only that surface
Answer and explanation in LearnFree account

29 more Histotechnology: processing, embedding and microtomy questions

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Histotechnology: processing, embedding and microtomy

Sections from a well-processed colon block come off wrinkled and about 20% shorter than the block face in the direction of cutting. The blade has already cut 40 blocks, and the trimmed block has sat for 20 minutes in a 30 °C room. What is the best correction?

The angle between the lower facet of the microtome knife and the face of the block is called the:

At the rotary microtome, paraffin sections come off one at a time instead of joining into a ribbon. A common cause is:

A transiliac bone biopsy is sent to measure osteoid seams in suspected osteomalacia. It should be embedded, without decalcification, in:

Which embedding medium is soluble in water, so that tissue can go into it without dehydration or clearing?

During an operation, a surgeon sends a hard, gritty fragment of a bony tumour for intraoperative diagnosis. The tissue cannot be cut in the cryostat. What is the best way to give a rapid opinion?

Leaving small biopsies in xylene for much longer than the schedule allows tends to make them:

Graded alcohols for a processor are prepared from 95% ethanol (rectified spirit). What volume of 95% ethanol, made up to 500 mL with distilled water, gives 70% ethanol?

Sections of a decalcified bone marrow trephine and of brain repeatedly float off plain glass slides during staining. They were picked up from a water bath with no adhesive and dried upright for 10 minutes at room temperature. Which change is most likely to prevent this?

Dioxane can replace both the alcohols and the clearing agent in paraffin processing because it:

A fresh lymph node block in the cryostat at -32 °C gives sections that crack and shatter into fragments. What is the best adjustment?

In a cryostat, the anti-roll plate:

A histology laboratory without air conditioning finds in the Kerala summer that its blocks soften and the sections compress and crumple at the microtome. Which change to the embedding wax helps most?

Large blocks, such as whole-brain slices or undecalcified bone in resin, are best cut on a:

A clearing agent extracted from citrus peel, used as a less toxic substitute for xylene, is:

Biopsies loaded on Friday evening finished processing at 2 a.m. Saturday and stayed in heated wax at 60 °C until Monday. Their blocks are hard and brittle and the sections crack and chatter. Biopsies from weekdays, processed and embedded at once, cut well. What prevents a repeat?

Commercial embedding waxes such as Paraplast contain added plastic polymers. Their main purpose is to make the wax:

Acetone dehydrates tissue within minutes, yet it is little used on routine processors. The main reason is that acetone:

On an ultramicrotome, a ribbon of epoxy sections floats on the trough, and each section shows a reflected interference colour. The sections are for routine transmission electron microscopy. Which colour shows the correct thickness?

Which clearing agent hardens tissue least and suits delicate tissues such as CNS, although it clears very slowly?

On a dry day in an air-conditioned room, paraffin ribbons cling to the blade holder and lift towards the operator's hands. Which simple measure helps most?

A renal biopsy is sent for direct immunofluorescence for immune-complex deposits. The core for this test should reach the laboratory:

A renal biopsy is sectioned at 5 µm like routine surgical blocks. On H&E and PAS, the glomeruli look crowded with nuclei and the basement membranes cannot be assessed. The pathologist suspects the appearance is artefact. What should the laboratory do?

At embedding, the tissue is placed with the surface to be examined facing down on the floor of the mould. Why?