• In fields of
fixation is a chemical
process by which biological tissues are
preserved from decay,thereby preventing
• Fixation terminates ongoing biochemical
• It also increase the mechanical strenght or
stability of treated tissues.
Which are to be fixed are following
Water and lipid soluble substances
• Crosslinking fixatives act by creating covalent chemical
bonds between proteins in tissue.
• Most commonly used fixative in histology is the crosslinking
fixative formaldehyde (also named formalin).
• Formaldehyde is the most commonly used fixative for amino
• Another popular aldehyde for fixation is glutaraldehyde.
• Glutaraldehyde fix proteins very rapidly.
• Glutaraldehyde may not penetrate thicker tissue
specimens as effectively as formaldehyde.
• Glutaraldehyde may offer a more rigid or tightly linked
• In order to demonstrate lipids,frozen sections
are commonly used.
used to preserve
• For preservation of lipids in cryostat sections
fixative should contain
• For this purpose we use the
• Fixation is over 3 days at room temperature.
• Alcoholic fixatives are used for glycogen
• Fixatives for ultrasturctural preservation of
dextrans and glycogen is
It is used by making stock solutions of
• Biogenic amines can be demonstrated in
tissues using a variety of techniques.
In this reaction potassium dichromateformaldehyde is used.
Formaldehyde fixation of the adrenal medulla
produced fluorescence of cells which
contained biogenic amines
fixed paraffin section
• Primary biogenic amines are well preserved
• Fixatives choosen for nucleic acids must depend upon
subsequent methods which are to be employed in
analysis of tissue.
–based fixatives (used but mostly
– (most widely used)
• It is to be used then the hydrolysis time varies with the
• For accurate demonstration of water soluble
substances,non-aqueous fixatives are used.
For example, Urates in gout
is a satisfactory fixative
Natural buffered formalin,
Alcoholic based fixatives