On Wed, 16 Feb 2000, Philip Oshel wrote:

> Well, yes, but this ignores the MeOH in formaldehyde, and it's because of
> the MeOH that us electron types use paraformaldehyde. (There, I condemned
> myself. I do do LM also, honest!)
> 
> And I made the mistake of trying to fix cultured macrophages with 10% NBF.
> Distorted them horribly, because of the methanol.

  Does the methanol really make all that difference? Conc. formalin
  contains about 10%, so there's only 1% in NBF. Back in 1968 or so,
  I remember seeing some pretty good EM pictures of human thyroid
  that had been surgically removed and had sat in NBF for some time.
  It was then osmicated etc. The work was done by my PhD supervisor, 
  the late Brian A. Young, in Birmingham (UK) and a student called
  David Kill, who went on to become a dentist. I'm pretty sure they
  published it - almost certainly in J. Anat. They also examined
  bits of thyroid fixed in glutaraldehyde and in Karnovsky-type 
  mixtures, which were better, but not impressively so.

  *** Has anyone done a severe comparison of 4% formaldehyde made from
  formalin vs paraformaldehyde, for EM or LM?  There are lots of
  anecdotes; mine is that I can't tell the difference for several
  LM applications. Others will surely disagree, but is this because
  of having made a controlled comparison?

  1% methanol might well be toxic to living (cultured) cells, but
  that's hardly a fault in a fixative. 1% ethanol would be below
  physiological levels; beer is 4% to 5%. 

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1