Lec 15: Dehydration
Why?
To remove water from tissues, and to replace with other solution
Tissues contain much "free" water which does not mix well with the paraffin used later in the procedure. Thus it must undergo alcohol dehydration
Materials are to be embedded in paraffin to facilitate microtomy and Paraffin was insoluble in water (hydrophobic) interfere microtomy
Most of the stains are used as alcoholic solutions, present of water might interfere staining process
Techniques
specimens are dehydrated in a graded ethanol series from water through 10%-20%-50%-95%-100% ethanol
To prevent large outflow of water can damage the morphology of the cells and tissues
Duration of dehydration
Tissue blocks 1 mm thick should receive up to 30 minutes in each alcohol
blocks 5 mm thick require up to 90 minutes or longer in each change
Types of dehydrating agents
Ethanol, Methanol, Acetone, butyl alcohol
Procedures
1) 50 % ethanol
2) 70 % ethanol
3) 95 % ethanol
4) 100 % ethanol
Partial dehydration: avoid loosing too much lipid from specimen