Histopath6

Drying

is the 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.

Methyl alcohol

Is a toxic dehydrating agent, primarily employed for blood and tissue films and for smear preparations.

Ethyl alcohol

is the alcohol recommended for routine dehydration of tissues. It is a clear, colorless, flammable fluid. It is considered to be the best dehydrating agent because it is fast-acting, it mixes with water and many organic solvents, and it penetrates tissues easily.

Butyl alcohol

which is utilized in plant and animal micro-techniques, is a slow dehydrating agent, producing less shrinkage and hardening than ethyl alcohol and is recommended for tissues which do not require rapid processing.

Clearing

Refers to the property of the solvents used- -when they have a relatively high refractive index and when tissue is immersed in them, the tissue becomes transparent and clear.

Blue discoloration of copper sulfate crystals

will indicate full saturation of dehydrating fluids with water.

78.3° C

Boiling point of ethanol

117.7° C

Boiling point of butanol

82.8° C

Boiling point of tertiary butanol

82.3° C

Boiling point of isopropanol

128° C

Boiling point of pentanol

56° C)

Boiling point of acetone

Acetone

It is a cheap, rapid-acting dehydrating agent utilized for most urgent biopsies which it dehydrates in 1/2 to 2 hours.
It is a clear, colorless fluid that mixes with water, ethanol and most organic solvents.

101.5°C

Bioling point of Dioxane

156.4° C

Bioling point of Cellosolve

215° C

Bioling point of Triethylphosphate

Tetrahydrofuran

Is a reagent that both dehydrates and clears tissues since it is miscible in both water and paraffin.

Xylene

is a colorless clearing agent that is most commonly used in histology laboratories.

Toluene

is better at preserving tissue structure and is more tolerant of small amounts of water left behind in the tissues than xylene. However, toluene is more expensive than and more toxic, so toluene is less commonly used.

Cedarwood oil

Is used to clear both paraffin and celloidin sections during the embedding process. It is especially recommended for central nervous system tissues and cytological studies, particularly of smooth muscles and skin. It requires two changes in clearing solution.

Aniline oil

This is not normally utilized as a routine clearing agent but it is recommended for clearing embryos, insects and very delicate specimens, due to its ability to clear 70% alcohol without excessive tissue shrinkage and hardening.

Impregnation (Infiltration)

is the process whereby the clearing agent is completely removed from the tissue and replaced by a medium that will completely fill all the tissue cavities and give a firm consistency to the specimen.

Embedding

is the process by which the impregnated tissue is placed into a precisely arranged position in a mold containing a medium which is then allowed to solidify

Paraffin

Is the simplest, most common and best embedding medium used for routine tissue processing.
It is a polycrystalline mixture of solid hydrocarbons produced during the refining of coal and mineral oils.

Vacuum embedding

involves wax impregnation under negative atmospheric pressure inside an embedding oven. It reduces the time when tissues are subjected to high temperatures thus minimizing heat-induced tissue hardening

Paraplast

Is a mixture of highly purified paraffin and synthetic plastic polymers, with a melting point of 56-57°C.

Embeddol

synthetic wax substitute similar to Paraplast with a melting point of 56-58°C. It is less brittle and less compressible than Paraplast

Celloidin

a purified form of nitrocellulose soluble in many solvents, suitable for specimens with large hollow cavities which tend to collapse, for hard and dense tissues such as bones and teeth and for large tissue sections of the whole embryo.