Re: Fixation Classification



--- Paul Bradbury  wrote: >
The first question that comes to mind is "Why do
> fixatives have to be 
> classified?" Do we routinely use such a great number
> that we have to put 
> them into categories?

I believe that through out the world, many fixatives
and different formulations are used. What about
Brasil's or Karnovsky's?

Pathologists classify everything. Why? I suppose it
makes it easier to predict behaviour of tumours or
diseases, or to easier understand the pathology. For
similar reasons classifying fixatives might make them
easier to understand or predict their behaviour.

> A fixative solution may contain several fixative
> agents each of which may be 
> additive or non-additive. Probably 99% of tissues
> are fixed in formaldehyde, 
> glutaraldhyde, alcohol, mercuric chloride, picric
> acid, potassium 
> dichromate, osmium tetroxide, or some combination of
> the above 6 reagents.
> Individually, the reagents may be classified
> according to any criteria we 
> choose to select (additive/non-additive,
> coagulant/non-coagulant, 
> gaseous/non-gaseous, colored/colorless,
> aldehyde/non-aldehyde, etc). But, 
> once the individual agents are combined, their
> individual classification is 
> meaningless.

Is it?

> We could, however, adopt the same
> approach used by wine 
> tasters; this fixative is "a well balanced blend of
> aldehyde, with a touch 
> of a coagulant heavy metal, a fine denaturing
> alcohol, and subtle tones of 
> picric acid".
> As to the sugestion of using the terms "soft and
> hard" fixatives based on 
> nuclear appearances, this leaves me totally
> confused! What on earth is a 
> "soft-fixed nucleus"?

Soft fixatives (such as the aldehyde fixatives), a/c
to Lee Luna renders the nucleus homogenous appearing
on H&E, whereas after hard fixatives the nuclei have
more pronounced chromatin and chromatin clumping is
more evident (eg picric acid, heavy metals, acidified

> Paul
> >From: Tony Henwood 
> >To: Histonet 
> >Subject: Fixation Classification
> >Date: Fri, 14 Dec 2001 09:17:36 +1100 (EST)
> >
> >Hi all,
> >Barry Rittman in August this year contributed to
> >histonet:
> >
> >"Fixatives used to be described as additive or non
> >additive.
> >Additive fixatives are those in which the fixing
> agent
> >  attaches to the
> >protein molecule.
> >Non additive fixatives on the other hand cause
> changes
> >in the proteins
> >that cause them to become changed, often used to be
> >described as
> >denaturation.
> >e.g. formalin., picric acid are  additive, ethanol
> is
> >non additive.
> >Because of the complexity of fixation and the great
> >variety of agents
> >used, the terms additive and non additive are not
> now
> >commonly used."
> >
> >The question I have been pondering is "What is the
> >preferred classification for fixatives that we
> should
> >use?"
> >Luna suggested the terms hard and soft fixatives,
> >basing his classification on nuclear appearance.
> >What does everyone else think?
> >
> >Regards and Happy Christmas and a good new year
> >

Tony Henwood JP BAppSc GradDipSysAnaly CT(ASC)
Laboratory Manager
Histopathology Department
The Childrens Hospital at Westmead
Locked Bag 4001
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