Having, due to gross carelessness,  dropped a muscle biopsy into formalin I
have to disagree.  When I hauled it back out,  after a few minutes, the
fibres had shrunk considerably.

Andy Shand

----- Original Message -----
From: J. A. Kiernan <jkiernan@julian.uwo.ca>
To: Jennings, Margaret A. <jennings@mayo.edu>
Cc: Histonet <histonet@pathology.swmed.edu>
Sent: Sunday, August 27, 2000 2:47 AM
Subject: Re: shrinkage


> On Fri, 25 Aug 2000, Jennings, Margaret A. wrote:
>
> >  What is the formula for shrinkage when using 10% neutral buffered
formalin
> > to fix  a tissue sample?
>
>   Aqueous formaldehyde (buffered or otherwise, with or without salts
>   to make it isotonic) does not change the volume of a specimen. For
>   details and references, read J.R.Baker's Principles of Biological
>   Microtechnique, a great classic in the field of fixation and staining.
>
> > If I start with a tissue a microns x  b microns x c
> > microns what do I end up with? Is there a time factor for additional
shrink?
>
>   The shrinkage of a formaldehyde-fixed block occurs during dehydration,
>   clearing, paraffin embedding and cutting and mounting the sections.
>   Linear dimensions in the plane of the section are typically 70 to 75%
>   of the the "fresh" sizes, with much variation among different organs.
>
>   If you cut cryostat sections and collect them onto slides or coverslips
>   they should be approximately life-size in the plane of the slide. The
>   vertical dimension shrinks with drying. Thick frozen sections, variously
>   processed before mounting onto slides, may go through large and
>   uncontrolable size changes. Flattening the section onto the slide with
>   a brush, prior to air-drying, can cause conspicuous expansion of the
>   area of a section.
>
>   The only way to know the amount of shrinkage is to measure the fresh
>   specimen and its equivalent dimensions in the stained and mounted
>   sections.
>
> > Is there also a formula for rate of penetration? Formalin infiltrates y
> > microns per t? What about other fixatives any formulas available?
>
>   The formula for depth penetrated is useful only for fixatives that
>   instantly cause a visible change as they diffuse into the specimen.
>   These are the coagulants, such as alcohol and mercuric chloride.
>   Baker's book says a lot about this, and provides data not published
>   elsewhere, as far as I know. Baker explained, with examples, that
>   in the case of formaldehyde the diffusion formula could not be
>   used, because the small molecules penetrated specimens rapidly but
>   reacted quite slowly to produce fixation, and the fixation did
>   not cause a visible change like that brought about by coagulant
>   fixatives.
>
>   Specimens should be fixed in formaldehyde (especially if neutral
>   and buffered, which slows down the reactions with protein) for
>   at least 24 hours to obtain reasonable fixation. For full
>   formalin fixation you need at least a week. Specimens dehydrated
>   after only a few hours in formaldehyde are fixed principally by
>   alcohol. Frozen sections cut after incomplete formaldehyde fixation
>   are just that: incompletely fixed. Often that's what's wanted,
>   especially in research work with the CNS.
>
>  John A. Kiernan,
>  Department of Anatomy & Cell Biology,
>  The University of Western Ontario,
>  LONDON,  Canada  N6A 5C1
>
>
>