CLEARING Flashcards
The process whereby alcohol or a dehydrating agents is removed from the tissue and replaced by a fluid (clearing agent) that will dissolve the wax with which the tissue must be impregnated
Clearing
Other term of Clearing
DEALCOHOLIZATION
This must be miscible with the dehydrating agent, paraffin wax, and mounting medium
Clearing agent
Ideal amount of clearing agent:
Not less than 10x the volume of the
tissue
Excellent and true clearing agent
Xylene
These are used when tissue is to be cleared directly from water
Glycerin and gum syrup
No de-alcoholization is involved in this process
Frozen section
This is added to each of the 95% ethanol baths part of dehydration process, acts as a softener for hard tissue
Phenol (4%)
Hard tissues can immersed in a __________ mixture or in ___________
glycerol/alcohol; “Molliflex”
TRUE OR FALSE:
Clearing agent should not make tissues transparent
FALSE. It SHOULD make tissues transparent
TRUE OR FALSE:
Most clearing agents are flammable liquids.
TRUE
Clearing fluids with a low boiling point are generally more readily replaced by
melted paraffin
This also affects the speed of penetration of the clearing agent.
Viscosity
Among the Common Clearing Agents Used are:
- Xylene (most common)
- Toluene
- Benzene
- Chloroform
- Cedarwood oil
- Aniline oil
- Clove oil
- Carbon tetrachloride
This causes the tissue to become brittle and
therefore more difficult to cut.
Prolonged exposure to most clearing agents
Used for clearing both for embedding and mounting procedures.
Xylene (Xylol)
Xylene is generally suitable for most routine histologic
processing schedules of less than 24 hours, and
the tissue block size is __________ in thickness.
less than 5 mm
For mounting procedures, it does not dissolve celloidin
Xylene
Evaporates quickly in paraffin oven, and can readily replaced by wax during impregnation and embedding
Xylene
Becomes milky when
incompletely dehydrated tissue is immersed in it.
Xylene
Not suitable for nervous
tissues and lymph nodes
Xylene
Used as a substitute for xylene or benzene
Toluene
Not carcinogenic. Tissues do not become excessively hard
and brittle even if left in in this clearing agent for 24 hrs.
Toluene
Tends to acidify in partially filled vessel. Highly concentrated solutions will emit fumes that are toxic upon prolonged exposure
Toluene
Preferred by some as clearing agent in the embedding process of tissues because it penetrates and clears tissues rapidly
Benzene
Excessive exposure may be extremely toxic to man and may become carcinogenic or it may damage the bone
marrow resulting in aplastic anemia.
Benzene
Rapid acting, recommended for urgent biopsies and routine purposes.
Benzene
Used for clearing of tissues during the embedding process, is slower in action than xylene, but causes less brittleness
Chloroform
Recommended for routine work. Recommended for tough tissue and for nervous tissues, lymph nodes and embryos because it causes minimum shrinkage and hardening of tissues.
Chloroform
Suitable for large tissue specimens
Chloroform
Does not make tissues transparent, evaporates quickly from a water bath, and tissue tend to float in this clearing agent
chloroform
Used to clear both paraffin and celloidin sections during the embedding process.
Cedarwood oil
Recommended for central nervous system tissues and cytological studies, particularly smooth muscles and skin
Cedarwood oil
Cedarwood oil requires ___________ in clearing solution, complete in 2-3 days
two changes
IDENTIFY:
1. Very penetrating
2. Miscible with 96% alcohol which it removes readily
3. Clears celloidin in 5-6 days
4. Makes tissue transparent
5. Improves cutting of the sections.
Cedarwood oil
Becomes milky upon prolonged storage and is very expensive
Cedarwood oil
Hard to be eliminated from the tissues in paraffin bath (oil to benzene for ½ hour) and Quality is not always uniform and good
Cedarwood oil
Not normally utilized as a routine clearing agent but is rather recommended for clearing embryos, insects and very delicate specimens, due to inability to clear 70% alcohol without excessive tissue shrinkage and hardening
Aniline oil
This reagent causes minimum shrinkage of tissues. Quality is not guaranteed due to its tendency to become adulterated.
Clove oil
Wax impregnation after clearing with clove oil is ________ and __________
slow; difficult
In this clearing agent, tissues become brittle, aniline dyes are removed, and celloidin is dissolved
Clove oil
Is used in clearing tissues for embedding. Its properties are very similar to chloroform although it is relatively cheaper.
Carbon tetrachloride
Disadvantage is the same as that of chloroform.
Produces considerable tissue hardening, and is dangerous to inhale on prolonged exposure due to its highly toxic effects
Carbon tetrachloride
These are slow-acting clearing agents
that can be used when double embedding techniques are required.
Methyl Benzoate/ Methyl Salicylate
Cedarwood clearing time:
2-3 days
Benzene clearing time:
15-60 minutes
Toluene clearing time:
1-2 hours
Xylene clearing time for urgent biopsies:
15-30 minutes
Xylene usual clearing time:
1/2 to 2 hours
Chloroform clearing time:
6-24 hours
