formaldehyde vs paraformaldehyde

[William Sun]

Hello all,

I am wondering about the difference between the above mentioned two compounds.
Our lab uses formulin (3.7% formaldehyde) to fix brains for histology.  
However, when the brains are sectioned for immunohistochemistry, most protocols 
call for 4% paraformaldehyde.  Is one preferable over the other?  Please reply
if you know the details.

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William Sun, Ph.D.                      Phone: (213)740-3406
Hedco Neuroscience Building             Fax: (213)740-5687
University of Southern California       Pager: (310)499-8670