CHAPTER 7: CHEMICAL FIXATIVES PART 4

Question 1

1. It fixes conjugated fats and lipids permanently by making them insoluble during subsequent treatment with alcohol and xylene. Fats form hydrated osmium dioxide, are stained black and therefore are easier to identify.
2. It preserves cytoplasmic structures well, e.g. Golgi bodies and mitochondria.
3. It fixes myelin and peripheral nerves well, hence, it is used extensively for neurological tissues.
4. It produces brilliant nuclear staining with safranin.
5. It adequately fixes materials for ultrathin sectioning in electron microscopy, since it rapidly fixes small
   pieces of tissues and aids in their staining
6. It precipitates and gels proteins.
7. It shows uniformly granular nuclei with clear cytoplasmic background
8. Some tissues (e.g. adrenal glands) are better fixed in vapor form of osmium tetroxide. This eliminates “washing out” of the fixed tissues
9. Completely permeabilizes cell
   membranes. The osmolarity of the fixative vehicle or solute is relatively unimportant
10. It penetrates tissue blocks in a gradient and in large samples the center of the block may not be as well fixed as the peripheral areas

Answer 1

Osmium Tetroxide (Osmic Acid; OsO4)

Question 2

T/F: Over-fixation with osmium tetroxide may result in extraction of cell components during dehydration and increases the hardness and brittleness of the tissue (for most tissues, 1mm blocks, should not be exposed to osmium for less than 0.5 or more than
1.5 hours).

Answer 2

True

Question 3

It is a poor penetrating agent, suitable only for small pieces of tissues (2-3 mm. thick).

Answer 3

Osmium Tetroxide

Question 4

It is a poor penetrating agent, suitable only for small pieces of tissues (2-3 mm. thick).

Answer 4

Osmium Tetroxide

Question 5

• It is readily reduced by contact with organic matter and exposure to sunlight, forming a black precipitate which settles at the bottom of the container.
• Prolonged exposure to acid vapor can irritate the eye, producing conjunctivitis, or cause the deposition of black osmic oxide in the cornea,
  producing blindness.

Answer 5

Osmium Tetroxide

Question 6

T/F: Osmium tetroxide inhibits eosin and makes counterstaining difficult

Answer 6

False (inhibits hematoxylin)

Question 7

Most common chrome-osmium acetic acid fixative used, recommended for nuclear preparation of such sections

Answer 7

Flemming’s Solution

Question 8

permanently fixes fat

Answer 8

Flemming’s Solution

Question 8

permanently fixes fat

Answer 8

Flemming’s Solution

Question 9

permanently fixes fat

Answer 9

Flemming’s Solution

Question 10

• Chromic-osmic acid combinations depress the
  staining power of hematoxylin (especially Ehrlich’s hematoxylin).
• It has a tendency to form artifact pigments; these may be removed by washing the fixed tissue in running tap water for 24 hours before dehydration.
• It is very expensive.

Answer 10

Flemming’s Solution

Question 11

Made up only of chromic and osmic acid, recommended for cytoplasmic structures particularly the mitochondria

Answer 11

Flemming’s w/o Acetic Acid