process of removing intercellular and extracellular water from the tissue following fixation and prior to wax impregnation
Dehydration
True or False
- Drying: removal of water by evaporation from a solid, semi-solid or liquid
- Dehydration: involves slow substitution of the water in the tissue with an organic solvent
True
True or False
- solid tissues should never be air dry
True
General Rule: whatever dehydrating agent is used, the amount in each step should not be less than ___ times the volume of the tissue in order to ensure complete penetration of the tissue by the dehydrating solution
not be less than 10 times
Temperature of ___°C will hasten dehydration time and is especially used for tissue sections that require urgent examinations such as fragmentary biopsies
37°C
True or False
- fixed tissues from water or aqueous fixative can directly transfer into absolute ethanol
False
- not advisable to transfer fixed tissues directly from water or aqueous fixative directly into absolute ethanol as it causes a rapid removal of water which can distort the appearance of more delicate cells and structures
- tissue may be stored in 70-80% alcohol
True or False
- concentrated alcohols (95% or absolute) tend to harden only the surface of the tissue while the deeper parts are not completely penetrated resulting in a relatively unequal impregnation and poor cutting of sections
True
- 70% or lower concentrations of alcohol, gradually increased to 95%, are used to avoid this
True or False
- In dehydration, smaller and more delicate tissues require lower concentrations and shorter intervals between changes
of succeeding descending grades of alcohol
False
- ascending grades of alcohol
It accelerates dehydration by removing water from the dehydrating fluid?
anhydrous copper sulfate
- ensure complete dehydration
_____ discoloration of copper sulfate crystals will indicate full saturation of dehydrating fluids with water
Blue discoloration
It is routinely use for dehydration of tissues including eyes and embryos
Ethanol (Ethyl Alcohol)
Boiling point of Ethanol?
78.3°C
Considered the best dehydrating agent?
Ethanol
- fast-acting, mixes with water and many organic solvents and penetrates tissues easily
- not poisonous and not very expensive
- miscible in all proportions with water
- extracts methylene blue and other thiazine dyes from sections, extracts more lipids than acetone
Used for blood and tissue films
and for smear preparations
Methanol (Methyl Alcohol)
- toxic dehydrating agent
Used in plant and animal microtechniques and tissues which do not require rapid processing
Butanol (Butyl Alcohol)
Boiling point of Butanol (Butyl Alcohol)
117.7° C
Used in staining series as a dehydrating agent
Tertiary Butanol (Butyl Alcohol)
- more expensive than butanol
- primary infiltration must be done in half tertiary butanol and half paraffin, prior to paraffin impregnation
- solidify at room temperature or below 25° C
Boiling point of tertiary
butanol (Butyl Alcohol)
82.8° C
Lillie considers it “the best all- around substitute for ethyl alcohol”
Isopropanol (Isopropyl Alcohol)
- cannot be used in the celloidin technic since nitrocellulose is insoluble in it
- cannot be used for preparing staining solutions, since dyes are not soluble in it
Boiling point of isopropanol?
82.3° C
Other name for pentanol
Amyl Alcohol
- miscible with 90% alcohol, toluene and xylene
- not miscible with water
- dissolves paraffin wax
- toxic, cannot be used in poorly ventilated rooms
Boiling point of pentanol
128° C
Use for urgent biopsies which it
dehydrates in 1/2 to 2 hours and use for small pieces of tissues
Acetone
- not recommended for routine dehydration
- cheap, rapid-acting dehydrating agent
- clear, colorless fluid that mixes with water, ethanol and most organic solvents
Boiling point for acetone
56° C
