Two hundred and forty negative-Pap smear slides are retrieved from the files. Half of
these slides were one-year old and the others were two-years old. Thirty slides from
each year are immersed in xylene with every four-hours checking until overnight. The
remaining 90 slides of each year are divided into 3 batches of 30 slides each. They
were put into the freezer with coverslip down for 10,20, and 30 minutes. The
coverslip removal was determined by coming off easily after slipped around the edges
by a razor blade.