STEP 3: CLEARING

Question 1

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

Answer 1

clearing

Question 2

in clearing, the tissue has a __________ appearance

Answer 2

transluscent

Question 3

clearing fluids with a ______________ are generally more readily replaced by melted paraffin

Answer 3

low boiling point

Question 4

affects the speed of penetration of clearing agents

Answer 4

boiling point
viscosity

Question 5

characteristics of a good clearing agent

Answer 5

1. Miscible with alcohol
2. Miscible with and easily removed by melted paraffin wax and/or by mounting medium 3. Shouldnotproduceexcessiveshrinkage,hardeningordamageoftissue
3. Does not dissolve out aniline dyes
4. Does not evaporate quickly in a water bath
5. Makes tissues transparent

Question 6

most commonly used clearing agent

Answer 6

xylene

Question 7

most rapid clearing agent (clears within 15-30 minutes); generally suitable for routine histologic processing schedules of less than 24 hours

Answer 7

xylene

Question 8

clearing agent that can be used for celloidin sections

Answer 8

xylene

Question 9

becomes milky when an incompletely dehydrated tissue is immersed in it

Answer 9

xylene

Question 10

may be used as a substitute for xylene or benzene

Answer 10

toluene

Question 11

recommended for routine purposes. it clears within 1-2 hours

Answer 11

xylene

Question 12

disadvantage: tends to acidify in a partially filled vessel

Answer 12

toluene

Question 13

clearing agent recommended for urgent biopsies (15-60 minutes) and routine purposes

Answer 13

benzene

Question 14

carcinogenic and damages bone marrow

Answer 14

benzene

Question 15

recommended for tough tissues (skin, fibroid and decalcified tissues), for nervous tissues, lymph nodes, embryos, and is suitable for large tissue specimens

Answer 15

chloroform

Question 16

disadvantage: tissues tend to float

Answer 16

chloroform

Question 17

disadvantage: does not make tissues transparent

Answer 17

chloroform

Question 18

disadvantage: not very volatile in paraffin oven

Answer 18

chloroform

Question 19

used to clear both paraffin and celloidin sections

Answer 19

cedarwood oil

Question 20

recommended for central nervous system tissues and cytological studies (smooth muscles and skin). clearing is completed in 2-3 days

Answer 20

cedarwood oil

Question 21

advantage: tissues may be left in oil without considerable damage and distortion, and it often improves cutting of the sections

Answer 21

cedarwood oil

Question 22

tissues cleared initially float before gradually staying to the bottom as clearing proceeds

Answer 22

cedarwood oil

Question 23

becomes milky upon prolonged storage

Answer 23

cedarwood oil

Question 24

recommened for clearing embryos, insects, and very delicate specimens

Answer 24

aniline oil

Question 25

its quality is not guaranteed due to its tendency to become adulterated. wax impregnation after clearing is slow and difficult.

Answer 25

clove oil

Question 26

its properties are very similar to that of chloroform althought it is relatively cheaper

Answer 26

carbon tetrachloride

Question 27

used when double embedding techniques are required

Answer 27

methyl benzoate and methyl salicylate