Dear Sylvia: If you work with an entire brain you are running the risk to be
manipulating under-fixed tissues, for how can you be sure that formalin has
penetrated to the organ's core? That's when dealing with small brains as
birds' we entirely cut them into serial transversal 3 mm. slices once they
have remained for 1 or more days  in 15 % formalin. Now we put the plastic
cassettes containing the tissues into 100 ml bottles filled with newly
prepared 15 % formalin, leaving them at room temp. or 37 ºC overnight and
they are ready for the authomatic processor. Please don't be afraid of
over-fixation: One night is the minimum time for fixation to be completed;
samples often rest for many days within their 100 ml. formalin bottles, even
for months, still we haven't had problems.  Our lab has been  working in a
TSE Project during several years, besides periodically processing avian
samples. The first thing you should do is to ensure a proper fixation,
secondly think of other causes of the problem. Our histotechnicians may be
very skillful, but at the beginning we've had the hell of a problem with the
authomatic processor. Let me put forward an example: Once we had a very
similar problem to yours, and it was due to insufficient impregnation of the
tissues in the successive reagents, including liquid paraffin. Do you know
how we solved the problem? Just lowering the amount of plastic cassettes in
the processor's containers, i.e. according to the maker the recipients had a
capacity for x cassettes, but our histotechnicians started reducing this
amount to 2/3 of the recommended one.
Dear colleague I hope to have been useful to you, and I also hope to have
some news of you from time to time, its so wonderful to exchange experiences
and knowledge with pathologists and histotechnicians sharing common goals.

Sincerely yours

Agustin Jose Venzano Halliburton
Pathology Group
INTA Castelar, Argentina
-----Mensaje original-----
De: Sylvia Kuhn 
Para: Agustín Venzano 
Fecha: Lunes, 25 de Marzo de 2002 02:09 p.m.
Asunto: RE: Cracks in paraffin sections