CHAPTER 7: CHEMICAL FIXATIVES PART 5

Question 1

• Used in 1-2% aqueous solution, usually as a constituent of a compound fixative
• It precipitates all proteins and adequately preserves carbohydrates

Answer 1

Chromic Acid

Question 2

• Used in a 3% aqueous solution
• Fixes bur does not precipitate cytoplasmic structures
• Preserves lipids
• Preserves mitochondria

Answer 2

Potassium Dichromate

Question 3

• Penetrates tissues well
• Harden tissues better and more rapidly than Orth’s fluid
• Recommended for the demonstration of chromatin, mitochondria, mitotic figures, Golgi bodies, RBC
  and colloid-containing tissues

Answer 3

Regaud’s (Muller’s) Fluid

Question 4

Disadvantages of Regaud’s (Muller’s) Fluid

Answer 4

1. It deteriorates and darkens on standing due to acidity; hence, the solution must always be freshly prepared
2. Penetration is slow, hence, tissues should not be thicker than 2-3 mm.
3. Chromate-fixed tissues tend to produce precipitates
   of sub-oxide, hence should be thoroughly washed in running water prior to dehydration
4. Prolonged fixation blackens tissue pigments, such as melanin; this may be removed by washing the tissues in running tap water prior to dehydration.
5. Glycogen penetration is poor; it is therefore, generally contraindicated for carbohydrates.
6. Nuclear staining is poor.
7. It does not preserve fats.
8. It preserves hemosiderin less than buffered formalin
9. Intensity of PAS reaction is reduced.

Question 5

• It is recommended for study of early degenerative processes and tissue necrosis.
• It demonstrates rickettsiae and other bacteria.
• It preserves myelin better than buffered formalin

Answer 5

Orth’s Fluid

Question 6

• For embryos and pituitary biopsies
• Preserves glycogen well but usually lyses
  erythrocytes.
• It is sometimes recommended for gastro-intestinal
  tract biopsies, animal embryos and endocrine gland tissue
• Excess picric should be washed from tissues prior to staining with 70% ethanol

Answer 6

Bouin’s Solution

Question 7

Advantages of Bouin’s Solution

Answer 7

1. It is an excellent fixative for glycogen
   demonstration.
2. It allows brilliant staining with the trichrome method.
3. It is suitable for Aniline stains (Mallory’s,
   Heidenhain’s or Masson’s methods)
4. It precipitates all proteins.
5. It is stable.

Question 7

Advantages of Bouin’s Solution

Answer 7

1. It is an excellent fixative for glycogen
   demonstration.
2. It allows brilliant staining with the trichrome method.
3. It is suitable for Aniline stains (Mallory’s,
   Heidenhain’s or Masson’s methods)
4. It precipitates all proteins.
5. It is stable.

Question 8

It causes RBC hemolysis and reduces the amount
of demonstrable ferric iron in tissue

Answer 8

Bouin’s Solution

Question 9

Picric acid is highly explosive when dry, and
therefore must be kept moist with distilled water or saturated alcohol at ______% concentration during storage.

Answer 9

0.5 to 1

Question 10

Bouin’s solution interferes with ____ method of staining; hence, tissues should be thoroughly washed with alcohol.

Answer 10

Azure eosin

Question 11

• For gastro-intestinal tract specimens and fixation of endocrine tissues
• Less lysis than Bouin’s

Answer 11

Hollande’s Solution

Question 12

• Improve upon aging
• Preservation of glycogen and carbohydrates
• It produces minimal distortion of micro-anatomical structures and can be used for general and special stains.

Answer 12

Gendre’s Solution

Question 13

Gendre’s Solution is the preferred fixative for tissues to be stained by ________ for collagen, elastic or connective tissue. (If tissue is fixed in formalin, a
pre-treatment in Bouin’s solution (as mordant prior to trichrome stain) is recommended

Answer 13

Masson’s trichrome

Question 14

T/F: Gendre’s Solution requires washing out.

Answer 14

False (does not require)

Question 15

Disadvantages of Gendre’s Solution

Answer 15

1. It is not suitable for fixing kidney structures, lipid and mucus.
2. It destroys cytoplasmic structures, e.g., mitochondria
3. It produces RBC hemolysis and removes demonstrable ferric iron from blood pigments.
4. It reduces or abolishes Feulgen reaction due to hydrolysis of nucleoproteins.

Question 15

Disadvantages of Gendre’s Solution

Answer 15

1. It is not suitable for fixing kidney structures, lipid and mucus.
2. It destroys cytoplasmic structures, e.g., mitochondria
3. It produces RBC hemolysis and removes demonstrable ferric iron from blood pigments.
4. It reduces or abolishes Feulgen reaction due to hydrolysis of nucleoproteins.

Question 16

It is better and less “messy” than Bouin’s solution and is an excellent fixative for glycogen.

Answer 16

Brasil’s Alcoholic Picroformol Fixative

Question 17

Acetic acid is not used alone for fixation but is incorporated into other fixatives to form a compound solution, most commonly at a concentration of
approximately ____%.

Answer 17

5

Question 18

• It fixes and precipitates nucleoproteins.
• It precipitates chromosomes and chromatin materials; hence, is very useful in the study of nuclear components of the cell. In fact, it is an essential constituent of most compound nuclear fixatives.
• It causes tissues (especially those containing collagen) to swell. This property is used in certain compound fixatives to counteract the shrinkage produced by other components (e.g. mercury)

Answer 18

GLACIAL ACETIC ACID

Question 19

T/F: When Glacial acetic acid is combined with Potassium Dichromate, the lipid-fixing property of the latter is destroyed (e.g. Zenker’s fluid)

Answer 19

True

Question 20

• It is recommended for acid mucopolysaccharides
• It fixes connective tissue mucin.
• It takes up CO2 to form insoluble lead carbonate especially on prolonged standing.

Answer 20

LEAD FIXATIVES

Question 21

• Also used as a decalcifier and fixative in microscopy
• Sometimes incorporated into compound fixatives
• It is a poor penetrating agent, hence, is suitable only for small pieces of tissues or bones.

Answer 21

TRICHLOROACETIC ACID

Question 22

Advantages of Trichloroacetic acid

Answer 22

1. It precipitates proteins
2. Its marked swelling effect on tissues serves to
   counteract shrinkage produced by other fixatives.
3. It may be used as a weak decalcifying agent.
4. Its softening effect on dense fibrous tissues facilitates preparation of such sections.

Question 23

Acetone is not recommended as morphological fixative for tissue blocks, mainly because of its shrinkage and poor preservation effects. Its use is reserved for the fixation of cryostat sections or for tissues in which enzymes have to be preserved.

a. TRUE/FALSE
b. FALSE/TRUE
c. BOTH TRUE
d. BOTH FALSE

Answer 23

c. BOTH TRUE

Question 24

• It is recommended for the study of water diffusible enzymes especially phosphatases and lipases
• It is used in fixing brain tissues for diagnosis of rabies.
• It is used as a solvent for certain metallic salts to be used in freeze substitution techniques for tissue blocks.

Answer 24

ACETONE (0-4 deg C)

Question 25

Disadvantages of Acetone

Answer 25

1. It produces inevitable shrinkage and distortion.
2. It dissolves fat.
3. It preserves glycogen poorly.
4. It evaporates rapidly.

Question 26

Provides a stable medium for transport of fresh unfixed tissues, such as renal, skin and oral mucosa biopsies, which will undergo subsequent frozen section and immunofluorescence studies

Answer 26

MICHEL’S SOLUTION