Dear Sylvia: Please call me Augustin. I'm a senior Vet Pathologist  having
initiated during several years as a Histotechnician. My expeience as a
Pathologist consists of 17 years of Livestock Pathology and 5 years of Avian
Pathology, reinforced through a fellowship stance in Tsukuba, Japan, in
1992/93. So your query sounds quite familiar to me
I'll tell you what we usually do with small birds:

First we moisten them with water plus detergent, cut into the medial side of
the legs and disrupt the coxofemoral joints, pull off the skin and feathers
and finally make a long ventral incision with the scalpel and withdraw the
lid off the skull with a scissors leaving the brain bare. Now we put the
entire bird into 15 % formalin, buffered or saline, leaving the bottles at
room temperature, never under refrigeration; if the weather is cold, we
leave the samples in a 37 ºC stove until next morning. Next morning we
complete the necropsy and section the organs 3 mm. thick.

Second we put the sliced tissues into their corresponding plastic cassettes
and these into bottles containing 15 % formalin as explained above.

Some details: We respect a sample volume/ fixative solution volume ratio=
1/10 in both stages.
                         We fix at room temp. or 37 ºC because cold hampers
formalin penetration, favouring Autolysis. Moreover, 37 ºC is a temp. quite
below the coagulation point of proteins, so it will respect the mollecular
structure of the tissues.
                         We use 15 % formalin because this concentration
ensures a readier fixation and our 40 % formalin is often precipitated,
having lost its original power.
                         We perform the original incisions on the body to
ensure the proper penetration of formalin into the different cavities,
including the skull.

                         Tissue cracks may have been due to two causes: Evil
fixation or the action of the bath water on the floating sections . With
respect to this latter point, my suggestion is to never surpass 38 ºC and to
leave the sections floating for a maximum of 1 to 2 minutes.

In our group Pathologists and Histotechnicians always join to deliberate on
every case, taking the first look of each section at the microscope together
to detect any eventual artifact. This is the only way to progress in
histopathology: to work united, to consult each other.

Yours sincerely

Agustin J. Venzano
Veterinary Histopathologist-Immunopathologist
Pathology Group-INTA Castelar, Argentina