Fixation:
Preservation of tissue in it is original condition, The most common fixative agents used in light microscopy is buffered formalin
Dehydration& clearing:
Removal of water from the tissue by a graded series of alcohol baths, beginning with 50% alcohol and progressing in graded steps to 100%
The tissue is then treated with xylene, a chemical that is miscible with melted paraffin. This process is known as clearing, because the tissue becomes transparent in xylene.