On Mon, 3 Jan 2000, Instrumedics, Inc. wrote:

> Does anyone have experience with coverslipping dehydrated sections
> without going through any clearing agent.

  Yes. The traditional way to go directly from alcohol to a
  resinous mounting medium, without clearing in xylene (or
  similar) is to use the mounting medium known as euparal,
  which mixes with alcohol and has quite a high refractive
  index, but not as high as that of Canada balsam or any of
  the modern synthetic resinous media. I tried euparal in
  the late 1960s and was not impressed, young though I was.
  Lillie & Fullmer's big textbook (1976) reviews media of this
  kind, and doesn't give them much of an endorsement. That's
  because Lillie was a pathologist who looked at stained
  sections. A medium like euparal is worthless for stained
  preparations. The purpose of staining is to generate
  contrast in color (or in black & white) while suppressing
  the specimen's intrinsic contrast, which is due largely to
  variations in refractive index.

  Euparal gets better press in the microscopy literature, where
  mounting media are not always expected to have the same
  refractive index as glass.

  For intelligent discussion of this, you should go to a
  library and look up Lillie's book. The 1965 edition was
  almost as thorough as the last (1975) one.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1
   E-mail: kiernan@uwo.ca