Gayle,
this situation arises because initially formalin kills the cells, produces
"temporary" bonds between various groups and then forms more permanent
"irreversible" bonds. the irreversible bond formation continues as long as
tissue is in formalin.
After the formation of the "temporary" or weak bonds, the process can be
reversed by procedures such as washing in water as this prevents the formation
of the irreversible bonds. Can give you more details if you wish.
Barry

Gayle Callis wrote:

> Have been a private discussion with someone, who brought up the point that
> fixation can reverse itself, and in the context of formalin?  but that the
> fixation process is eventually irreversible.
>
> Any comments on this, I found it interesting, and know the other party is
> looking in.
>
> I have never experienced this, or even heard of it happening, but am always
> ready for enlightenment, could be something I have missed in reading,
> listening or discussion.
>
> Gayle Callis
> Veterinary Molecular Biology
> Montana State University
> Bozeman MT 59717-3610
> 406 994-4705
> 406 994-4303