Histology

• 1. Kill the tissue (prevent autolysis)
• 2. Maintain relationship b/w cells and extracellular substance
• 3. Increase differences in Refractive Index to increase the contrast b/w different tissue elements
• 4. Enhance staining (w/ exceptions)
• 5. Rendering cell constituents insoluble (especially proteins)
• 6. Make tissue firmer iot make gross dissection easier

• 1. Inactivate enzymes
• 2. Kill bacteria/molds
• 3. Make tissue more receptive to dyes
• 4. Modify tissue constituents for the maximum retention of form throughout processing

• 1. Pyknotic, over-stained nuclei
• 2. Loss of enzyme activity
• 3. Loss of antigenicity
• 4. False localization of nucleic acids
• 5. Lysis of RBCs

• 1. Heat
• 2. Desiccation

Air drying of touch preps for Wright staining

• 1. Physical
• 2. Chemical

• 1. Additive/Non-additive
• 2. Coagulant/Non-coagulant

They chemically link to - and change - the tissue

• Mercuric chloride
• Chromium trioxide
• Picric acid
• Formaldehyde
• Glutaraldehyde
• Osmium tetroxide
• Zinc sulfate/chloride

MCPFGOZ

• Acetone
• Alcohols

They dissociate bound water molecules from tissue protein groups

Non-additive Fixatives

They establish a network in tissue allowing solutions to readily penetrate the interior of the tissue

The create a gel, making penetration by solutions difficult

• Mercuric chloride
• Picric Acid
• Zinc salts
• Acetone
• Ethyl alcohol
• Methyl alcohol
• Cupric sulfate

MPZAEMC

• Formaldehyde
• Glutaraldehyde
• Osmium tetroxide
• Potassium dichromate
• Glyoxam

Acetic Acid

• nucleic acids - coagulant
• cytoplasm - non-coagulant

Temperature - increase => increased rate of fixation and autolysis

Size of specimen - larger specimen => longer to penetrate and fix

Volume Ratio - should be 15 - 20 x more fixative than tissue volume

Time - depends on tissue size/type and fixative