A few more worms for the barrel. I'd add that Barry's comments and the
earlier ones by Freida Carson are for light microscopy (which is probably
what you're interested in). Processing for electron microscopy adds new
wrinkles, especially when drying specimens for SEM--popular for bone
specimens. Shrinkage then also depends on the drying method used, for both
final shrinkage and range in the amount of shrinkage. Freeze-drying often
leads to shrinkage of around 40% (all my measurements are linear, not
volume), but may range from roughly 30/35% to 60%. Critical Point drying
has less range in the final size, but usually leads to about 50%.
Hexamethyldisilizane is even more consistent than CPD, but also leads to
about 50% shrinkage. Then there's air-drying, drying from water, EtOH,
acetone ... all of which work best for some specimens.

Mind, these numbers are all arm-waving to some extent because of all the
variables already mentioned, and because tissues prepared for SEM keep
drying and shrinking in storage, if stored properly. If not, they absorb
water and expand.

Then, just for that extra added worm, to elaborate on Barry's comment below
"...differential shrinkage with different tissue components." This depends
at least partially on the mechanical properties of different tissues, and
may not be, and usually isn't, isotropic. Meaning shrinkage may be
different in the x-, y-, and z-axes depending on, for instance, the
orientation of collagen fibers, or any other tissue/tissue component that
varies in structure with direction.

The best way to measure any biological specimen is alive and screaming in a
light microscope. Any processing will change its dimensions. Even then, if
the osmolarity isn't right... .

(Then there's the table I remember seeing, but can't remember where, that
measured changes in tissue volume as the sample was passed through an EtOH
dehydration series. First the tissue expanded until about 70% EtOH, then it
shrunk. My apologies to the person who did this for not remembering who
they are.)

Phil

>Cliff,
>            "please open barrels of worms carefully".
>The degree of shrinkage that is encountered with soft tissues is generally
>quoted
>as 25-30%. This varies considerably between different tissues and within
>tissues.
>It depends, as Frieda has pointed out, on the fixative used, duration of
>fixation
>and type and length of processing procedure as well as the composition of the
>tissue and the phase of the moon.
>Generally, hard tissues that have been decalcified tend to shrink to a lesser
>degree than soft tissue as can be seen from separation of these in
>sections. With
>hard tissue, acids in general can  swell tissues but there is usually
>considerable
>greater swelling in the subsequent washing.
>Baker's data provides a useful starting point for comparison of fixatives
>but as
>it mostly uses gelatin and albumen blocks, cannot take into account the
>differential shrinkage with different tissue components.
>Other  important points to consider are the degree of compression when
>cutting the
>section and the partial  recovery of some tissues such as collagen when the
>section is mounted on a water bath. Measurement of shrinkage from tissue
>sections
>is difficult  as section thickness is then another factor. It may be best to
>surface stain the block and measure tissues and  compare to cut surface of the
>original unfixed block if posible.
>For frozen sections,  soft tissue shrinkage is generally quoted as 2% and for
>celloidin processing as 4-5%.
>Barry


****be famous! send in a tech tip or question***
Philip Oshel
Technical Editor, Microscopy Today
PO Box 620068
Middleton, WI  53562
(608) 833-2885
oshel@terracom.net