1. Fixation and Fixative
Prepared by : Reem Aldossari

2. THE GENERAL VISCRA OF THE RAT

3. Definition of Fixation
In the fields of histology, pathology, and cell biology, fixation is a chemical process by which biological tissues are preserved from decay, either through autolysis or putrefaction.
Fixation terminates any ongoing biochemical reactions, and may also increases the mechanical strength or stability of the treated tissues.

4. Purpose of fixation
The purpose of fixation is to preserve a sample of biological material (tissue or cells) as close to its natural state as possible in the process of preparing tissue for examination. To achieve this several conditions must usually be met.
The aims of fixation are:
Prevent postmortem (PM) degeneration
Prevent autolysis. It is effective against hydrolytic enzymes
Stop the bacterial effect
Harden the tissues, as fixation causes coagulation of proteins
Fixation has a mordanting effect, facilitating subsequent staining of tissues.

5. Features of fixatives
First, a fixative usually acts to disable intrinsic biomolecules – particularly proteolytic enzymes – which would otherwise digest or damage the sample.
Second, a fixative will typically protect a sample from extrinsic damage. Fixatives are toxic to most common microorganisms (bacteria in particular) which might exist in a tissue sample or which might otherwise colonise the fixed tissue.
Finally, fixatives often alter the cells or tissues on a molecular level to increase their mechanical strength or stability.
This increased strength and rigidity can help preserve the morphology (shape and structure) of the sample as it is processed for further analysis such as Nuclear Morphometry System.

6. Characteristics of a good fixative
It must kill the cell quickly without shrinkage or swelling
It must penetrate the tissue rapidly
It must inhibit bacterial decay and autolysis
Harden the tissue and render it insensitive to subsequent treatment as staining
It should allow tissue to be stored for long time
It should be simple to prepare and economical is use.

7. Preparation of fixatives:
Neutral buffered formalin 10%:
Tap water ml
formalin (40%=100%) ml

8. Thank you
for your attention