Process whereby the impregnated tissue is placed into a precisely arranged position in a mold

4 types of impregnation and embedding medium

Simple, most common and best embedding medium used for routine tissue processing

Paraffin wax is solid at room temperature but its melting point is

Most common melting point of paraffin wax for histological use

Temperature to decrease viscosity and improve infiltration of the tissue

Paraffin wax is traditionally marketed by what melting points

Which common waxes is normally used for routine work

Ways by which paraffin wax impregnation and embedding may be performed

Requires at least 4 changes of wax at 15 mins intervals

Only 2-3 changes of wax, rapid diagnosis with less technicality

An automatic tissue processing machine

The frequency with which fluids are changed depends on the number and sizes of the tissues processed

The presence of odor in the clearing agent during final paraffin wax bath indicates that the paraffin wax needs to be changed

Dehydrating fluids should be changed frequently

The first 100% ethanol bath should be discarded

The clearing agent and the dilute ethanols should be changed at least once a week

Wax bath thermostats should be set at least 3°C above the melting point of the wax

Involves wax impregnation under negative atmospheric pressure. Recommend for urgent biopsies.

Vacuum infiltration consists of

Requires a vacuum infiltrator or embedding oven to which a vacuum of up to 760 mm Hg is applied

Time required for complete impregnation in vacuum embedding

Which gives the fastest results among the 3 methods of paraffin wax impregnation

Tissues should not be left in the paraffin oven for more than

Paraffin oven must be maintained at a temperature of

Coarse filter paper for wax

Substitutes for paraffin wax

Highly purified paraffin and synthetic plastic polymers.

Melting point: 56 - 57°C

Winter: 54 - 56°C

Summer: 60 - 63°C

Less brittle and less compressible

Melting point: 56 - 58°C

A semisynthetic wax recommended for embedding eyes

Produce of paraffin and containing rubber

Not soluble in water but soluble in 95% ethyl alcohol

Melting point: 46 - 48°C

Used for impregnation without prior clearing of tissue

May be used as clearing agent in Ester wax

Are plastic polymers, mostly polyethylene glycols

Melting point: 38 - 42°C or 45 - 56%

Most commonly used polyethylene glycol

True on carbowax

Will reduce tissue distortion and promote flattening and floating out of sections

Proprietary blends of plastic polymer paraffin waxes reduces infiltration times and facilitates thin sectioning

Purified form of nitrocellulose

Suitable for specimens with large hollow cavities, hard and dense tissues, and whole embryo

Recommend for bones, teeth, brain, whole organs

Ether and alcohol: 12 - 24 hrs

Thin celloidin (2-4%): 5 - 7 days

Medium celloidin (4-6%): 5 - 7 days

Thick celloidin (8-12%): 3 - 5 days

Preferred for processing whole eye sections

Equal parts of chloroform and cedarwood oil

More explosive than celloidin

Plasticizers that prevent tissues from cracking in LVN

Rarely used except when dehydration is to be avoided. It is water soluble and does not require dehydration and clearing

Serves to prevent the growth of molds

The process by which a tissue is arranged in precise positions in the mold

Types of blocking out molds

2 L shaped strips

Series of interlocking plates resting on a flat metal base

Special stainless steel base mold

Disposable embedding mold

Disposable thin plastic embedding molds, available in 3 different sizes

Recommend for busy routine laboratories

Embedding celloidin blocks but are useful for paraffin wax blocks. Cheap and easy to make.

X is drawn with soft lead pencil on the inner surface of the bottom

Types of celloidin

Types of plastic (resin)

Recommended for embedding hard tissues such as bones, teeth and eyes

Used to control the rate or evaporation of solvent

Process by which tissues are first embedded or fully infiltrated with a supporting medium such as agar or nitrocellulose, then infiltrate a second time with paraffin wax

Made up of a balance mixture of epoxy plastic, catalysts, and accelerators

Originally introduced for electron microscopy in the mid 1950s, now seldomly used

Made up of esters of acrylic or methacrylic acid, and are used extensively for light microscopy

Types of epoxy

Low viscosity mixture which provides rapid infiltration of tissues

A carcinogenic component of epoxy

Types of acrylic

A catalyst that decomposes to form phenyl radicals acting as an active site for the polymerization of acrylics

Process whereby alcohol is removed from the tissue

Most common clearing agent

Used when the tissue is to be cleared directly from water

Has a lower boiling point than xylene but takes longer to clear

Affects the speed of penetration of the clearing agent

Clearing time of xylene

Better at preserving tissue structures. Substitute for xylene and benzene

Clearing time of toluene

Penetrates amd clears tissues rapidly. Highly carcinogenic and strongly discouraged

Clearing time of benzene

Clearing agent that does not become translucent. Can process thicker tissue blocks

Clearing time of chloroform

Clears both paraffin and celloidin sections. Recommend for CNS and Cytological studies

Clearing time of cedarwood oil

Recommended for embryos, insects, and very delicate specimens

Tissues become brittle, aniline dyes are removed, and celloidin is dissolved

Similar to chloroform but cheaper

Ability to perform two processes at the same time, dehydrating and clearing

Miscible both with water and paraffin. Used primarily when time is important

Found in essential oils. Earliest transition solvents to be used

Found in citrus peels such as lemons and oranges

Lowest hazard rating of all xylene alternatives

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

Process of removing intercellular and extracellular water from the tissue

Removal of water by evaporation from a solid, semi-solid, or liquid

General rule of dehydration:

Amount in each step should not be less than __ the volume of the tissue

Commonly used dehydrating agents

Solutions utilized to make dehydration possible. Alcohols of various types. Used in increasing strengths to remove aqueous tissue fluids with little disruption to the tissue caused by diffusion currents

Anhydrous fluid can be used as a dehydrating agent for the

reason that

Recommended alcohol for routine dehydration of tissues.

Clear, colorless flammable liquid

Fast-acting and penetrates tissues easily

Not poisonous and not very expensive

Toxic dehydrating agent

Primarily employed for: blood & tissue films and for smear

preparations

Slow dehydrating agent

Utilized in plant & animal micro-techniques

Recommended for tissues which do not require rapid processing

A temperature of 37C will hasten dehydration time required for urgent examinations such as

Boiling point of 78.3C

Boiling point of 117.7C

Boiling point of 82.8C

Universal solvent

Boiling point of 82.3C

The best all-around substitute for ethyl alcohol

Boiling point of 128C

Boiling point of 56C

For urgent biopsies which it dehydrates in 30 mins to 2 hours

Boiling point of 101.5C

Excellent dehydrating and clearing agent

Boiling point of 156.4C

Combustible at 110-120F

Boiling point of 215C

Used to dehydrate sections and smears following certain stains

Also a dehydrating and clearing agent. May cause conjunctival irritation

As a transition fluid

A good substitute for propylene oxide