Jerry Meade, University Laboratories Detroit [MI] Medical Center asks: 

>>What is STF fixative? What is its composition?<<

About five years ago (have I really been on Histonet that long?) Hal Hawkins, 
hal@utmb.edu, posted:

>>We have been very pleased with the results of immunostaining tissues fixed 
with Streck Tissue Fixative (Streck Labs Inc., PO 37625, Omaha, NE 
68137-0625, (402) 691-7453).  

It contains Bronopol, which is 2-bromo-2-nitro-propanediol, and diazolidinyl 
urea, C7H14N4O7, with zinc sulfate and sodium citrate, and less than 0.1% 
formaldehyde. It meets government standards for disposal in public sewers, as 
not forming hazardous vapors, and for shipping as a nontoxic substance. 
Prolonged fixation does not mask antigens. I presume it is a weak 
cross-linker and denaturant. The morphology is excellent at the light level, 
but no good by EM.<<

If I understand correctly, fixatives like this are basically holding media 
that keep tissue from deteriorating before it fixes in the alcohols (or 
formalin) in the processor. Good for keeping inspectors and managers happy.

Bob Ri