[Histonet] Silly Question?

[Pat Flannery]

Please humor me on this if it's obvious (to everyone but me):  why do  
we use paraformaldehyde (which is so inconvenient to make up) rather  
than buffered formalin or just diluted formaldehyde itself?

It seems that around here, some folks prefer paraformaldehyde (either  
2% or 4%) and others use formalin, while some others stick to diluted  
formaldehyde (I see all 4 on labels for specimens submitted for  
histology).  Is it mostly a matter of personal preference or where you  
were trained (i.e. force of habit) or is there a valid reason to use  
each solution (basically the same chemical once in solution, merely  
buffered or not)?  The only answer I've gotten when I've asked is,  
"That's what we always use."

Thanks.

-Pat Flannery (not a "real" histologist - I just play one in the lab)