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?

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. 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"?


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
>
>
>
>
>=====
>Tony Henwood JP BAppSc GradDipSysAnaly CT(ASC)
>Laboratory Manager
>Histopathology Department
>The Childrens Hospital at Westmead
>Locked Bag 4001
>WESTMEAD, 2145
>AUSTRALIA
>
>http://shopping.yahoo.com.au - Yahoo! Shopping
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