one of the steps in tissue processing

1. Infiltration
(Impregnation)

2. • It is the process where clearing agent is completely
removed from the tissue.
• Giving a firm consistency to the specimen
• Easier handling and cutting of suitably thin sections
without any damage or distortion to the tissue and its
cellular components.

3. *3 TYPES OF TISSUE IMPREGNATION
1. Paraffin wax impregnation
- Simplest, most common and best embedding medium used for routine
tissue processing.
2. Collodion/ Celloidin impregnation
- Purified form of nitrocellulose soluble in many solvents, suitable for
specimens with large hollows cavities which tends to collapse, for hard and
dense tissue (teeth and bones).
3. Gelatin impregnation
- Rarely used.
- Used for delicate specimens and frozen tissue sections because it prevents
fragmentation.

4. 1. PARAFFIN WAX IMPREGNATION
Advantages: Disadvantages:
1. Thin individual serial sections may be
cut with ease from the majority of tissues
without undue distortion.
1. Overheated paraffin makes the specimen
brittle.
2. The process is very rapid, allowing
sections to be prepared within 24 hours.
2. Prolonged impregnation will cause
excessive tissue shrink age and hardening,
making the cutting of sections difficult .
3. Tissue blocks and unstained mounted
sections may be stored in paraffin for an
indefinite period of time after
impregnation without considerable tissue
destruction.
3. Inadequate impregnation will promote
retention of the clearing agent. Tissues
become soft and shrunken, and tissue
blocks crumble when sectioned and break
up when floated out in a water bath.
4. Many staining procedures are permitted
with good results.
4. Tissues that are difficult to infiltrate
needs long immersion for proper support;
otherwise they will crumble on sectioning.
5. Paraffin processing is not recommended
for fatty tissues.

5. 2. CELLOIDIN IMPREGNATION
Advantages: Disadvantages:
1. It permits cutting of tissue sections which are
thicker than in paraffin wax, and is therefore
recommended for processing of neurological
tissues.
1. Very slow (lasting for several days or weeks)
2. Its rubbery consistency allows tissue blocks
that are either very hard or of varying
consistency, to be cut without undue distortion.
2. Very thin sections are difficult to cut.
3. Dense tissues which are hard to infiltrate
(bones and brain) and specimens which tend to
collapse easily due to air spaces (eyes)
3. Serial sections are difficult to prepare.
4. It does not require heat during processing
hence producing minimum shrinkage and tissues
distortion specially for cutting large bones
sections.
4. It is very volatile and therefore must be kept in
bottles with ground-glass stoppers to prevent
evaporation.

6. * 3 METHODS FOR CELLOIDIN
IMPREGNATION OF TISSUE:
1. Wet Celloidin Method
- Recommended for bones, teeth, large brain sections
and whole organs.
2. Dry Celloidin Method
- Preferred for processing of whole eyes sections.
3. Nitrocellulose Method
- Another form of celloidin soluble in equal concentration
of ether and alcohol with a lower viscosity, allowing it to
be used in higher concentrations and still penetrates
tissues rapidly.

7. 3. Gelatin Impregnation
- It is water-soluble and does not require dehydration and clearing
- After the fixative has been completely washed out, the tissue is placed in
10% Gelatin with 1% Phenol for 24 hrs., transferred to 20% Gelatin with 1%
Phenol for the next 12 hrs. and finally to another fresh solution of 20%
Gelatin with 1% Phenol which is then allowed to cool in refrigerator until
impregnation and embedding are completed.
- Tissues should not be more than 2-3 mm thick since Gelatin embedded
specimens are harder to freeze than un-impregnated tissues.
- 1% Phenol serves to prevent the growth of molds.