[Histonet] re: overprocessing

[Carl Hobbs]

Thank you for  your comments, John.
My first post was under a guy called Ted Brain who was always looking into 
processing /embeding protocols and reagents in an attempt to find the 
"optimal " for our bone and teeth!
It was years ago when I taught Histopathology that I would use , in a simple 
( OK, plagiarised)  practical on "The effects of Fixation" , 1cm  cubes of 
gelatin, fixed using a range of coagulant/additive fixing fluids to 
demonstrate the penetration rates and the physical effects that the 
different fixing agents had on pure protein. A qualitative assessment 
only....... wouldn't expect more from students at 7.30pm after they'd been 
at college since 10am.
Regarding my initial remark: I didn't notice any shrinkage difference 
between the short-time fixed gelatin blocks and the ones that had been fixed 
for ages. But then again, there is the effect of alcohol in the processor 
which is significant. I wasn't doing this comparison under rigid exptl 
conditions: we have many perfused- formalin fixed specimens which  have been 
embedded in gelatin, vibratome-cut and that  I then wished to process to 
pwax. Would extended fixation time of the gelatin "stiffen" it sufficiently 
to prevent shrinkage? The answer , for me, is "No". So, I take off the 
gelatin, before processing.
No "exact science" there, Rene. Sorry!
Carl