Page 411 - The Veterinary Laboratory and Field Manual 3rd Edition

380 Susan C. Cork

are important species differences. Farmed species optimize this procedure and the tissue sections
can include reptiles (for example, crocodiles), fish produced are generally of a high quality. A range
and a number of different avian species (for exam- of stains can be used to highlight specific cellu-
ple, ducks, geese, quails) as well as fur species lar structures and/or invading microorganisms.
(for example, mustelids and other carnivores) Standard stains such as Haematoxylin and Eosin
and large mammals (such as equids, elephants (H&E) are routinely used but often additional
1
and camelids) used for power and transport. sections will be cut and stained with specialized
Veterinary and other animal health staff should stains such as Gram stain for bacteria, Giemsa
become familiar with the normal anatomy of for haemoprotozoa and Young’s fungal for fungal
the species that are commonly handled in their hyphae. Stained slides can be mounted using a
region. Practical training in conducting a necropsy mounting agent to seal a cover slip in place and
should be delivered by an experienced veterinary will remain in good condition for many years.
professional and due care should be taken with
regard to biosafety and biosecurity.
Neutral buffered formalin
(fixation time 12–24 h)
8.3 Histopathology
• Formalin (40% aqueous solution of form-
tissues from post-mortem cases aldehyde) 100 ml
• Sodium dihydrogen orthophosphate
Histology is defined as the study of tissues. (monohydrate) 4 g
Histopathology is the study of abnormal tis- • Disodium hydrogen orthophosphate
sues. It is necessary to be familiar with the (anhydrous) 6.5 g
normal structure of tissues before pathological • Distilled water 900 ml
changes can be recognized. Histopathological
examination can be useful to confirm a diagno- Neutral buffered formalin is suitable for
sis but it may be too expensive to be justified most histological purposes and is preferable
in routine examinations. The preparation of his- to formal saline as the formation of formalin
tology slides requires skill and experience and pigment in tissues is avoided. The solution
the interpretation of slides requires specialized is isotonic so specimens can be stored in
training. To ensure good quality sections tissues this fluid. Typically, a sample should be fixed
must be fixed in 10% buffered formalin (see box) in 10x the volume of fixative relative to the
although for some tissues other fixatives may volume of the sample.
be recommended (consult specialized reference
texts or an expert for more detail). Once fixed,
tissues are then cut, processed and blocked ready tissues from biopsy samples
for sectioning and staining. In most cases an area
of tissue which has normal and abnormal cells Tissue samples may be collected from live ani-
will be chosen for section preparation. The tis- mals but these are usually limited to skin sections
sue sections are then set in paraffin wax and cut collected using aseptic collection methods under
into thin slices using a microtome which is usu- local or general anaesthesia. These samples are
ally set at 2–5 µm. The sectioned tissues are then usually referred to as biopsy samples. The tech-
put onto microscope slides and stained. There niques used are outlined in standard surgical
are a range of automated systems available to text books and should only be performed by suit-

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