On Sat, 23 Sep 2000 Jakrobsmith@aol.com wrote:

> Does anyone else out there in histoland not put PTA in their martius yellow? 
> Any comments would be appreciated.

  It doesn't make sense to do so, in terms of the conventional wisdom of
  trichrome staining or the various less conventional theories. If your
  observation is really true, it may mean that the older ideas are wrong,
  and we need to re-think the way these stains work.

  The obvious First Test is to find out if the effect of adding PTA to
  the martius yellow solution changes anything other than the pH. Check
  the pH of your martius yellow with & without PTA (which will acidify
  the solution). Use hydrochloric or sulphuric acid to make a solution
  with the same pH, and see if all that phosphorus and tungsten really
  makes any difference.  Lillie did experiments of this kind, and was
  not impressed with the notion of PMA and PTA as "colourless acid dyes"
  promoted by J.R.Baker. I think most other investigators would
  disagree with Lillie on this one.

  PTA (or PMA) attaches to collagen and displaces medium-size dye
  anions (usually red) from it, but doesn't do the same for
  cells (except for certain secretory granules). For reasons that
  aren't glaringly obvious, PTA allows the largest dye anions of
  the trichrome mixture (usually aniline blue or fast green FCF)
  to bind fairly selectively to collagen. The smallest dye
  anions (orange or yellow) ideally localize only in red
  blood cells and certain secretory granules. Quite a good
  argument can be made for the case that these objects are
  too densely textured to admit and retain dye ions of 
  different sizes, so they preferentially retain the smaller
  ones.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1
   Phone: (519) 661-2111
   FAX (Department): (519) 661-3936
   E-mail: kiernan@uwo.ca