Dehydration, Clearing & Wax Impregnation. Dr.Samah Kotb Nasr Eldeen. Dehydration. Dehydration:-. Is the first stage in processing after fixation. Is the removal of water and some of the lipid tissue fluids. This is done by many compounds.
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Dr.SamahKotb Nasr Eldeen
Most of these compounds are alcohols. Some of these are hydrophilic and remove water from the tissues; but others dehydrate by repeated dilution of the aqueous tissue fluid.
Anhydrous Copper Sulphate (ACS) or called white copper sulphate is added to the last dehydrated bath to:
1. Check the presence of water when it changes to blue.
2. Elongate the life of the alcohol.
Acetone: it is used when time is important i.e to speed up dehydration. No dilutions. Generally, it is used for urgent manual processing.
3) Dioxine: (di ethylene dioxide) also used to speed up dehydration. Sometimes used for manual processing but it has many disadvantages:
Most of the clearing agents are flammable. Generally those of the low boiling point are rapidly removed by paraffin wax more than those of higher boiling point.
The removal of clearing agents by paraffin wax is enhanced under vacuum (not complete vacuum) because this will affect the tissue.
Xylene, Toluene & Benzene
Cedar wood oil
Soft wax has lower melting point whereas the hard wax has a higher melting point. The temperature should not exceed 2 – 3º C the melting point of the wax.
Some substances are added to paraffin wax in different ratio to modify the wax consistency and its melting point. These include:
Manual: For routine and urgent cases. This takes a long time. Prolong immersion should be in a tolerant fluid. Its now taken over by automation.
Automatic processing: carried on by automatic machines. It takes less time and it has the following advantages:
Reduced pressure can be applied to speed up wax impregnation.
Paraffin wax of variable melting points can be used for embedding. This depends on the type of the tissue. If the tissue is hard; high melting point wax is used whereas low melting point wax is used with soft tissues.
Most blocks cut from the largest area of the tissue but there are some exceptions: