Sections of a blood-rich spleen fixed for 3 days in unbuffered formalin show fine brown-black granules over red cell areas. The Perls stain is negative. The best next step is to:

Treat the sections with alcoholic picric acid

Bleach the sections with potassium permanganate

Treat the sections with iodine and thiosulfate

Report the granules as hemosiderin

Fixation prevents autolysis mainly by:

Inactivating the tissue's own enzymes

Dissolving the lipids in the cells

Histotechnology: fixation and decalcification

26 Kerala PSC Lab Technician Gr II practice questions on Histotechnology: fixation and decalcification, 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 of a blood-rich spleen fixed for 3 days in unbuffered formalin show fine brown-black granules over red cell areas. The Perls stain is negative. The best next step is to:
1. ATreat the sections with alcoholic picric acid
2. BBleach the sections with potassium permanganate
3. CTreat the sections with iodine and thiosulfate
4. DReport the granules as hemosiderin
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Answer: A · Treat the sections with alcoholic picric acid
Acid formaldehyde hematin (formalin pigment) forms when acidic, unbuffered formalin acts on hemoglobin, so it is heaviest in blood-rich tissue and after long fixation. It lies as fine brown-black, birefringent granules over red cell areas, and a negative Perls stain shows it is not hemosiderin. It is removed by treating the sections with saturated alcoholic picric acid before staining. Using 10% neutral buffered formalin prevents it.
- B: Permanganate bleaching is used for melanin, not formalin pigment.
- C: Iodine and thiosulfate remove mercury pigment, which forms only after mercuric fixatives.
- D: A negative Perls stain rules out hemosiderin.
Question 2 · Medium
Fixation prevents autolysis mainly by:
1. AInactivating the tissue's own enzymes
2. BMaking the tissue transparent
3. CDissolving the lipids in the cells
4. DRemoving water from the tissue
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Answer: A · Inactivating the tissue's own enzymes
Autolysis is self-digestion of tissue by its own enzymes, released from lysosomes after the cells die. Fixatives such as formaldehyde cross-link proteins, including these enzymes, and alcohols coagulate them, so digestion and bacterial putrefaction stop. Fixation also hardens the tissue so that it withstands processing. Tissue should go into fixative as soon as it is removed, because delay causes autolytic changes, most of all in gut mucosa.
- B: Making tissue transparent is clearing, which follows dehydration.
- C: Lipid loss is a side effect of solvents, not the aim of fixation.
- D: Removing water is dehydration, a later processing step.
Question 3 · Easy
How does EDTA remove calcium from bone?
1. AAcid dissolution
2. BIon exchange
3. CElectrolysis
4. DChelation
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Answer: D · Chelation
EDTA binds calcium ions into a soluble complex, a process called chelation, and removes calcium from the surface of the bone crystals layer by layer. It works at a neutral pH, so it is slow (days to weeks) but gentle. It preserves morphology, enzymes, antigens for immunohistochemistry and DNA better than acids. It is the decalcifier of choice when special tests are needed on the tissue.
- A: Acids such as nitric and formic acid dissolve calcium salts; EDTA works at neutral pH.
- B: Ion-exchange resins are added to formic acid to take up the released calcium.
- C: Electrolysis drives calcium ions out of bone with an electric current in acid.
Question 4 · Easy
Which fixative contains mercuric chloride, potassium dichromate and glacial acetic acid?
1. AZenker's fluid
2. BHelly's fluid
3. CCarnoy's fluid
4. DBouin's fluid
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Answer: A · Zenker's fluid
Zenker's fluid is an aqueous solution of mercuric chloride and potassium dichromate, with glacial acetic acid. Helly's fluid has the same base but formalin replaces the acetic acid. Both leave a mercury pigment that is removed from sections with iodine followed by sodium thiosulfate. Mercury is toxic, so these fixatives are now little used and their waste needs special disposal.
- B: Helly's fluid has formalin in place of acetic acid.
- C: Carnoy's fluid is absolute ethanol, chloroform and glacial acetic acid.
- D: Bouin's fluid is picric acid, formalin and acetic acid.
Question 5 · Easy
Tissue fixed in Bouin's fluid is stained yellow by its content of:
1. AMercuric chloride
2. BPicric acid
3. CPotassium dichromate
4. DGlacial acetic acid
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Answer: B · Picric acid
Bouin's fluid is saturated aqueous picric acid with formalin and glacial acetic acid. Picric acid is yellow and colors the tissue; the excess is washed out in 70% alcohol before processing. Bouin's fluid gives good nuclear detail and is used for testis and gastrointestinal biopsies and before trichrome stains. Dry picric acid is explosive, so stock is always kept moist.
- A: Mercuric chloride is in Zenker's and Helly's fluids and leaves a dark pigment, not a yellow color.
- C: Potassium dichromate is in Zenker's and Helly's fluids, not in Bouin's.
- D: Acetic acid is colorless; it swells tissue and offsets shrinkage.
Question 6 · Medium
Which method gives the most accurate end point of decalcification?
1. AChemical test for calcium
2. BProbing with a needle
3. CBending the specimen
4. DRadiography (X-ray)
Answer and explanation in LearnFree account
Question 7 · Medium
Which fixative acts by coagulating proteins rather than by forming cross-links between them?
1. AFormaldehyde
2. BEthanol
3. CGlutaraldehyde
4. DOsmium tetroxide
Answer and explanation in LearnFree account
Question 8 · Hard
Used nitric acid from a femoral head under decalcification is neutralized with ammonia, and saturated ammonium oxalate is added. Within 30 minutes it turns cloudy. What should be done?
1. AChange the acid and continue decalcifying
2. BNeutralize the bone in sodium sulfate
3. CReturn the bone to fresh formalin
4. DStop and process the bone at once
Answer and explanation in LearnFree account
Question 9 · Easy
Carnoy's fluid is a rapid fixative valued mainly for preserving:
1. ALipids
2. BGlycogen
3. CRed blood cells
4. DMitochondria
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Question 10 · Hard
How much commercial formalin (37-40% formaldehyde) is needed to prepare 2 litres of 10% formalin?
1. A200 mL
2. B500 mL
3. C20 mL
4. D100 mL
Answer and explanation in LearnFree account
Question 11 · Easy
Which is NOT a property of an ideal fixative?
1. AIt penetrates the tissue rapidly
2. BIt keeps the tissue soft and pliable
3. CIt prevents autolysis and putrefaction
4. DIt causes little shrinkage or swelling
Answer and explanation in LearnFree account
Question 12 · Medium
Which decalcifying agent works fastest, but spoils nuclear staining if bone is left in it too long?
1. ANeutral EDTA
2. BFormic acid
3. CTrichloroacetic acid
4. DNitric acid
Answer and explanation in LearnFree account
Question 13 · Hard
Sections of spleen fixed in Zenker's fluid show coarse black granules scattered over the tissue and the empty spaces alike. Treatment with alcoholic picric acid does not remove them. What are they, and how are they removed?
1. AMercury pigment; iodine then thiosulphate
2. BHemosiderin; dilute acid
3. CMelanin; hydrogen peroxide
4. DFormalin pigment; alkaline alcohol
Answer and explanation in LearnFree account
Question 14 · Medium
Why is formalin fixation of a large specimen slow, even though formalin penetrates fairly quickly?
1. AIt needs heat to start acting
2. BCross-links form slowly after penetration
3. CIt acts only at an acid pH
4. DIt penetrates slowly but fixes at once
Answer and explanation in LearnFree account
Question 15 · Easy
Which fixative is traditionally preferred for testicular biopsies?
1. AZenker's fluid
2. B10% formalin
3. CBouin's fluid
4. DCarnoy's fluid
Answer and explanation in LearnFree account
Question 16 · Medium
Which substance is added to the mercuric chloride-dichromate base, in place of acetic acid, to make Helly's fluid?
1. AFormalin
2. BChloroform
3. CEthyl alcohol
4. DPicric acid
Answer and explanation in LearnFree account
Question 17 · Medium
Why must picric acid be stored moist under water?
1. ADry picric acid is radioactive
2. BIt loses its colour when dry
3. CIt absorbs moisture and spoils
4. DDry picric acid is explosive
Answer and explanation in LearnFree account
Question 18 · Easy
The volume of fixative used should be about how many times the volume of the tissue?
1. AEqual volume
2. B2-3 times
3. C15-20 times
4. D100 times
Answer and explanation in LearnFree account
Question 19 · Hard
A laboratory needs 750 mL of 10% (v/v) formic acid for decalcification and has 90% formic acid in stock. How much stock is needed?
1. A83.3 mL
2. B67.5 mL
3. C8.3 mL
4. D75.0 mL
Answer and explanation in LearnFree account
Question 20 · Easy
The fixing action of formaldehyde on tissue proteins is best described as:
1. ADehydration of cells
2. BCoagulation of proteins
3. CExtraction of lipids
4. DFormation of methylene bridges
Answer and explanation in LearnFree account
Question 21 · Medium
A femoral head is put straight into 5% nitric acid from theatre without prior fixation. What is the main risk?
1. AFormalin pigment formation
2. BFaster calcium removal
3. CAcid damage to unfixed tissue
4. DHarder blocks to cut
Answer and explanation in LearnFree account
Question 22 · Medium
A bone biopsy from a suspected metastasis will need immunohistochemistry and molecular tests. Which decalcifier should be used?
1. A5% nitric acid
2. BFormic acid-sodium citrate
3. CEDTA
4. DPerenyi's fluid
Answer and explanation in LearnFree account
Question 23 · Easy
Formalin pigment in sections can be removed by treating them with:
1. AAlcoholic picric acid
2. BLugol's iodine
3. CSodium thiosulphate
4. DHydrogen peroxide
Answer and explanation in LearnFree account
Question 24 · Easy
The most widely used routine fixative in histopathology is:
1. AZenker's fluid
2. BBouin's fluid
3. CCarnoy's fluid
4. D10% neutral buffered formalin
Answer and explanation in LearnFree account
Question 25 · Medium
Why is formalin buffered to a neutral pH for routine fixation?
1. ATo stain the nuclei blue
2. BTo remove fat from tissue
3. CTo prevent formalin pigment
4. DTo speed up decalcification
Answer and explanation in LearnFree account

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Histotechnology: fixation and decalcification

Sections of a blood-rich spleen fixed for 3 days in unbuffered formalin show fine brown-black granules over red cell areas. The Perls stain is negative. The best next step is to:

Fixation prevents autolysis mainly by:

How does EDTA remove calcium from bone?

Which fixative contains mercuric chloride, potassium dichromate and glacial acetic acid?

Tissue fixed in Bouin's fluid is stained yellow by its content of:

Which method gives the most accurate end point of decalcification?

Which fixative acts by coagulating proteins rather than by forming cross-links between them?

Used nitric acid from a femoral head under decalcification is neutralized with ammonia, and saturated ammonium oxalate is added. Within 30 minutes it turns cloudy. What should be done?

Carnoy's fluid is a rapid fixative valued mainly for preserving:

How much commercial formalin (37-40% formaldehyde) is needed to prepare 2 litres of 10% formalin?

Which is NOT a property of an ideal fixative?

Which decalcifying agent works fastest, but spoils nuclear staining if bone is left in it too long?

Sections of spleen fixed in Zenker's fluid show coarse black granules scattered over the tissue and the empty spaces alike. Treatment with alcoholic picric acid does not remove them. What are they, and how are they removed?

Why is formalin fixation of a large specimen slow, even though formalin penetrates fairly quickly?

Which fixative is traditionally preferred for testicular biopsies?

Which substance is added to the mercuric chloride-dichromate base, in place of acetic acid, to make Helly's fluid?

Why must picric acid be stored moist under water?

The volume of fixative used should be about how many times the volume of the tissue?

A laboratory needs 750 mL of 10% (v/v) formic acid for decalcification and has 90% formic acid in stock. How much stock is needed?

The fixing action of formaldehyde on tissue proteins is best described as:

A femoral head is put straight into 5% nitric acid from theatre without prior fixation. What is the main risk?

A bone biopsy from a suspected metastasis will need immunohistochemistry and molecular tests. Which decalcifier should be used?

Formalin pigment in sections can be removed by treating them with:

The most widely used routine fixative in histopathology is:

Why is formalin buffered to a neutral pH for routine fixation?