Clearing Flashcards
the transition step between
dehydration and infiltration with the
embedding medium
clearing
Process whereby alcohol is removed from the tissue & replaced with a substance that will dissolve the wax with which the tissue is impregnated (Paraffin) or the medium on which the tissue is to be mounted.
de-alcoholization or clearing
Does not dissolve aniline dyes
- cedarwood oil
- ## xylene
Most commonly used clearing agents are
Xylene, dioxane, chloroform and cedarwood oil
The clearing agent will make microscopic tissue preparations transparent due to
high index refraction
Characteristics of a Good Clearing Agent
- Miscible with alcohol to promote rapid removal for the dehydrating agent
- Should be miscible with and easily removed by melted paraffin wax.
- Should not produce excessive shrinkage, hardening or damage of tissue
- Should not dissolve out aniline dyes
- Should not evaporate quickly in a water bath
- Should make tissues transparent
Xylene clearing time
30 mins to 1 hr
Makes tissues transparent
- xylene
- benzene
- cedarwood oil
Colorless clearing agent that is most commonly used. Most rapid clearing agent,
xylene
Not suitable for nervous tissues and lymph nodes
xylene
Tissues do not become excessively hard and brittle even if left for 24 hrs
toluene
suitable for urgent biopsies
xylene
Expensive
- toluene
- cedarwood oil
- clove oil
What is the clearing time of toluene
1- 2 hours
It is preferred as clearing agent in the embedding process of tissue
benzene
Slower in action than xylene but causes less brittleness
chloroform
Acts fairly rapidly and is recommended for routine purpose
toluene
Does not make tissues hard and brittle but it causes minimum shrinkage
benzene
highly flammable
- xylene
- benzene
clearing time of benzene
15 mins to 1 hr
not carcinogenic / toxic
- ## toluene
becomes milky when an incompletely dehydrated tissue is
immersed in it
xylene
carcinogenic / toxic
- benzene
- chloroform
- carbon tetrachloride
does not make tissues transparent
- ## chloroform
It may damage the bone marrow resulting in aplastic anemia
benzene
Suitable for large tissue specimens. Thicker tissue blocks (up to 1 cm) are can be
processed
chloroform
chloroform clearing time
6-24 hours
not recommended for routine purposes
- cedarwood oil
- aniline oil
- clove oil
Relatively toxic to the liver after prolonged inhalation
chloroform
Difficult to remove from paraffin sections because it is not very volatile
chloroform
Recommended for clearing embryos, insects and very
delicate specimens due to its ability to clear 70% alcohol
without excessive tissue shrinkage and hardening
aniline oil
Complete clearing is difficult to evaluate
chloroform
cedarwood clearing time
2-3 days
Very penetrating clearing agent
cedarwood oil
Recommended for central nervous system tissues and cytological studies
cedarwood oil
Becomes milky upon prolonged storage and should be filtered before use
cedarwood oil
its quality is not guaranteed due to its tendency to become adulterated
clove oil
Tissues become brittle, aniline dyes are removed and celloidin is
dissolve
clove oil
produces considerable tissue hardening and dangerous to
inhale on prolonged exposure due to its highly toxic effect
Carbon Tetrachloride
Slow-acting clearing agents that can be used when double
embedding techniques are required.
Methyl Benzoate and
Methyl Salicylate
