STEP 3: CLEARING Flashcards
or de-alcoholization is the process whereby alcohol or a dehydrating agent is removed from the tissue and replaced with a substance that will dissolve the wax which the tissue is to be impregnated or the medium on which the tissue is to be mounted
clearing
in clearing, the tissue has a __________ appearance
transluscent
clearing fluids with a ______________ are generally more readily replaced by melted paraffin
low boiling point
affects the speed of penetration of clearing agents
boiling point
viscosity
characteristics of a good clearing agent
- Miscible with alcohol
- Miscible with and easily removed by melted paraffin wax and/or by mounting medium 3. Shouldnotproduceexcessiveshrinkage,hardeningordamageoftissue
- Does not dissolve out aniline dyes
- Does not evaporate quickly in a water bath
- Makes tissues transparent
most commonly used clearing agent
xylene
most rapid clearing agent (clears within 15-30 minutes); generally suitable for routine histologic processing schedules of less than 24 hours
xylene
clearing agent that can be used for celloidin sections
xylene
becomes milky when an incompletely dehydrated tissue is immersed in it
xylene
may be used as a substitute for xylene or benzene
toluene
recommended for routine purposes. it clears within 1-2 hours
xylene
disadvantage: tends to acidify in a partially filled vessel
toluene
clearing agent recommended for urgent biopsies (15-60 minutes) and routine purposes
benzene
carcinogenic and damages bone marrow
benzene
recommended for tough tissues (skin, fibroid and decalcified tissues), for nervous tissues, lymph nodes, embryos, and is suitable for large tissue specimens
chloroform
disadvantage: tissues tend to float
chloroform
disadvantage: does not make tissues transparent
chloroform
disadvantage: not very volatile in paraffin oven
chloroform
used to clear both paraffin and celloidin sections
cedarwood oil
recommended for central nervous system tissues and cytological studies (smooth muscles and skin). clearing is completed in 2-3 days
cedarwood oil
advantage: tissues may be left in oil without considerable damage and distortion, and it often improves cutting of the sections
cedarwood oil
tissues cleared initially float before gradually staying to the bottom as clearing proceeds
cedarwood oil
becomes milky upon prolonged storage
cedarwood oil
recommened for clearing embryos, insects, and very delicate specimens
aniline oil
its quality is not guaranteed due to its tendency to become adulterated. wax impregnation after clearing is slow and difficult.
clove oil
its properties are very similar to that of chloroform althought it is relatively cheaper
carbon tetrachloride
used when double embedding techniques are required
methyl benzoate and methyl salicylate
