On Thu, 6 Apr 2000, Gamal Badawy wrote:
 
> I'm looking for an answer to this question:
> What is the role of acetic acid in Bouin's fixative and is it
> essential to be included in the formula for histology?
 
  The acetic acid coagulates DNA and provides a characteristic
  sharply defined pattern of chromatin distribution, often
  characteristic for different cell-types. It also causes
  swelling of the tissue (especially collagen), which is
  counteracted by the picric acid in the mixture. Picric acid
  combines with and coagulates proteins generally. The
  formaldehyde cross-links proteins, mostly after they have
  been coagulated, so it won't do much if you fix in Bouin
  for only a few hours. A days is better, BUT with long
  immersion the two acid components attack nucleic acids,
  with extraction of RNA and production of aldehyde groups
  in DNA (which becomes Schiff-positive). Anionic dyes work
  well after Bouin (for reasons that could be discussed but
  are largely speculative). Nuclei, however stained, are much
  more pleasing to look at after Bouin (or other acetic acid
  containing fixatives) than after neutral formaldehyde.
 
> Gamal Badawy
> Faculty of Science
> School of Biosciences
> University of Birmingham
 
   I'm a Brum graduate, but there wasn't a School of
   Biosciences in my time. Have they lumped some
   traditional departments together?
 
 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1