CLEARING

Question 1

Process whereby alcohol or a dehydrating agent is removed from the tissue and replaced with a substance that will dissolve the wax with which the tissue is to be impregnated (e.g. paraffin) or used as the medium on which the tissue is to be mounted (e.g. Canada balsam)

Answer 1

Clearing

Question 2

Clearing is also known as?

Answer 2

de-alcoholization

Question 3

Most commonly used clearing agent

Answer 3

Xylene

Question 4

used when the tissue is to
be cleared directly from water, as in a frozen section, no de-alcoholization is involved in this process

Answer 4

Glycerin and Gum Syrup

Question 5

Clearing agent should be miscible with _________ to promote rapid removal of the dehydrating agent from the tissue

Answer 5

alcohol

Question 6

True or False
- prolonged exposure to most clearing agents causes the tissue to become brittle and therefore more difficult to cut

Answer 6

True

Question 7

Other term for xylene

Answer 7

Xylol

Question 8

Colorless clearing agent that is most commonly used in histology laboratories

Answer 8

Xylene
- mostly used as a clearing agent during tissue processing and as a dewaxing agent during staining
- used in cover slipping, in cleaning tissue processors, as solvent to remove synthetic immersion oil from the microscope objective and in recycling of used slides

Question 9

Intermediate products of xylene metabolism that cause toxicities

Answer 9

methyl benzaldehyde

Question 10

True or False
- It is highly recommended that all chemicals be stored on eye level so cracking or leaking containers are immediately visible and there is less potential for chemicals falling onto lab workers when pulling from shelves.

Answer 10

False
- stored below eye level

Question 11

Clearing agent routinely used and for urgent biopsies

Answer 11

Xylene (Xylol)

Question 12

Most rapid clearing agent

Answer 12

Xylene

Question 13

Clearing time for xylene

Answer 13

15-30 minutes

Question 14

Xylene becomes ______ when an incompletely dehydrated tissue is immersed in it

Answer 14

milky

Question 15

Clearing time of toluene

Answer 15

1-2 hours

Question 16

Not carcinogenic clearing agent

Answer 16

Toluene

Question 17

Clearing agent better at preserving tissue structure and is more tolerant of small amounts of water left behind in the tissues than xylene

Answer 17

Toluene
- more expensive than xylene and more toxic
- less commonly used
- substitute for xylene or benzene for clearing both during embedding and mounting processes

Question 18

Used to be a popular routine clearing agent until recently
when its highly carcinogenic properties were recognized

Answer 18

Benzene
- miscible with absolute alcohol
- volatilizes rapidly in paraffin oven, therefore easily eliminated from the tissue
- carcinogenic

Question 19

Clearing agent that damage the bone marrow resulting in aplastic anemia

Answer 19

Benzene

Question 20

Clearing time of benzene

Answer 20

15-60 minutes

Question 21

Clearing agent use for tough tissues (e.g. skin, fibroid and decalcified tissues) for nervous tissues, lymph nodes and embryos

Answer 21

Chloroform
- slower in action than xylene, but causes less brittleness
- thicker tissue blocks (up to 1 cm) can be processed
- miscible with absolute alcohol
- causes minimum shrinkage and hardening of tissues
- not inflammable

Question 22

Clearing time of chloroform

Answer 22

6-24 hours

Question 23

Clearing agent that is toxic to the liver after prolonged inhalation

Answer 23

Chloroform
- does not make tissues transparent
- tissues tend to float in chloroform, avoided by wrapping the tissues with absorbent cotton gauze to facilitate sinking of the section in solution

Question 24

Clearing agent use for central nervous system tissues and cytological studies, particularly of smooth muscles and skin. Also clear acetic-alcohol fixed tissues

Answer 24

Cedarwood Oil
- requires two changes in clearing solution
- very penetrating
- miscible with 96% alcohol which it removes readily

Question 25

True or False - Cedarwood oil does not dissolve out aniline dyes

Answer 25

True

Question 26

Clearing agent use for embryos, insects and very delicate specimens

Answer 26

Aniline Oil - ability to clear 70% alcohol without excessive tissue shrinkage and hardening

Question 27

Very similar to chloroform but cheaper

Answer 27

Carbon Tetrachloride

Question 28

Superior to ordinary dehydrating and clearing agents due to its ability to perform two processes at the same time, thereby shortening the total processing time and allowing more time for fixation. It is non-toxic but offensive odor

Answer 28

Tetrahydrofuran

Question 29

Used primarily when time is important because the tissues may be embedded with paraffin within 4 hours after fixation

Answer 29

Dioxane - tissues are transferred to dioxane straight from Bouin's fluid or formalin fixative - causes greater shrinkage than xylene does - dangerous and toxic to human especially to the liver

Question 30

Isoprene polymers found in essential oils originally derived from plants, though some are now synthesized

Answer 30

Terpenes

Question 31

Earliest transition solvents to be used in histology and include turpentine and oils of bergamot, cedarwood, clove, lemon, oreganum and sandalwood

Answer 31

Terpenes

Question 32

A substitutes from the terpene family. It is volatile oil found in citrus peels which goes by several trade names and a natural oil found in the skins of citrus fruits, such as lemons or oranges

Answer 32

Limonene

Question 33

Offer the clearing action with the lowest hazard rating of all xylene alternatives

Answer 33

Orange Oil Based Clearing Agents - excellent for preserving fine tissue structure, and can often be used in place of xylene with no alteration of protocol

Question 34

Government regulations have restricted most of the effective solvents in this class

Answer 34

Chlorinated Hydrocarbons

Question 35

An efficient substitute for xylene, non-hazardous, less expensive and causes less shrinkage of the tissue

Answer 35

Coconut Oil - used as a dealcoholization agent in the histopathological laboratory, without losing the quality of the histological details - only drawback associated with coconut oil is its tendency to get solidified at a lower temperature

Question 36

Clearing agent that is nontoxic, nonhazardous, nonflammable, biodegradable, economic, easy to handle, and readily available

Answer 36

Bleached Palm Oil - clearing agent during tissue processing and as a dewaxing agent during staining gives good tissues, sections and histological slides