1. Quantity - at least 15 to 20 volumes of the fixative should be used for every volume of tissue.

2. Penetration - No fixative will penetrate more than 2 to 3 mm of solid tissue of 0.5cm of porous tissue in a 24 hour period.

3. Thickness - Thickness would depend on the type of tissue, but no specimen should be more than 4mm for good fixation. 3mm is preferable.

4. Time - Most tissues should remain in fixative fro 24 hours and should then be stored in 70% alcohol.

5. Temperature - most fixation is done at room temperature ( 25°C) but can be done for longer periods of time at 4°C

6. Primary purpose - Fixation is primarily the stabilization of proteins, which must be rendered insoluble for satisfactory fixation.

7. Heat - Heat will coagulate protein, but is not recommended for fixation since it also speeds autolysis.

8. Special fixatives - These are used to be sure the pathologic lesion is fixed and can be demonstrated in the finished slide.

9. Remember never to store picric acid in a dry form since it is highly explosive when dry.

1. Use for exceptionally bloody specimens such as infacts and congested spleen

2. Use for unusual tumors such as rhabdomyosarcoma and malignant teratomas

3. Use for viral inclusions such as Negri Bodies

4. Recommended for the preservation of tissue on which Feulgen Plasma reaction is done.

5. Never use metal forceps or metal containers when handling any tissue fixed in mercurial fixatives.

6. excellent trichromes after this fixative

7. Omit the acetic acid and add it to the stock solution when ready to use.

8. An artifact pigment is formed with this mercuric uric fixative. Remove during staining sequence with the iodine -sodium thiosulfate sequence.

9. For excellent phoshotungstic acid-hematoxylin stains, tissues must be fixed in Zenker's fluid.

1. This fixative is known as Zenker's formol, since it uses the same basic stock solution and formalin is not added to the stock until just before use to prevent a dark brown precipitate from forming.

2. Excellent for bone marrow including preservation of red blood cells.

3. An artifact pigment is formed with this mercuric fixative which must be removed during the staining sequence, with the iodine-sodium thiosulfate sequence.

4. Excellent for blood-forming organs

5. Excellent for intercalated discs

1. RNA must be fixed in this fixative in the methyl green pyronine technique is done

2. Never use this fixative if acid-fast bacilli are to be demonstrated, since the bacilli are rendered non-acid-fast

3. Carnoy's fluid hemolizes the red cells and dissolved acid-soluble cell granules and pigments

4. Nissl granules are well preserved in Carnoy's fluid.

5. Glycogen storage disease is preserved with fixation in carnoy's fluid.

1. The most widely used fixing agent for pathologic histology is formaldehyde.

2. Formaldehyde is commercially available at 37% to 40% gas in water, sold as formalin. These fluids are regarded as 100% formalin and the 10% solutions contains 4.1 to 4.5% of the formaldehyde gas and a 20% solution contains 8.2 to 9% of the formaldehyde gas.

3. Solutions of formalin diluted with distilled water are commonly acid from small amounts of formic acid as a manufacturing impurity or from the oxidation of the gas.

4. NBF should not be prepared by storage after calcium carbonate or magnesium carbonate, since the fluid drawn off for fixation promptly becomes acid.

5. NBF should be prepared by the addition of a soluble buffer to prevent the formation of formalin pigment.

6. Fixation in formalin is influenced by the concentration of the reagent and by temperature. 10% fixes are adequate in 48 hours at room temperature.

7. Many special stains are excellent after NBF fixation since it is compatible with most stains.

8. 10% formalin is the best fixative for tissues for fat stains since fewer artifacts are seen in the oil-red O stains after this fixative.