Page 116 - The Veterinary Laboratory and Field Manual 3rd Edition

The selection, use, maintenance and quality control of laboratory equipment and supplies 85

fungal growth, especially in moist circum-
stances.
• Ideally, microscopes should be housed in a
suitable acclimatized room. This is because of
the risk of condensation forming within the
optics of the microscope if temperatures fluc-
tuate significantly. Local air humidity can be
diminished by placing an electrical dehumid-
ifier, or even more simply, by placing dried
silica gel crystals, near the microscope if it is
stored in a closed cupboard.
• Always make sure that some spare light bulbs
for the microscope are in stock and keep the
reference numbers of all parts and accessories
for replacing them if necessary.
• Use a small soft brush to clean less accessible Figure 2.48 The microscopic field is divided accord-
places. ing to the plate of a clock. Photo: Idzi Potters, ITG,
• Do not mix immersion oils. Antwerp, Belgium.
• Decontaminate the stage with 70% alcohol.
• Turning off: turn the lamp to its lowest set- Systematic examination
ting, switch off.
The search for eggs and larvae of helminths and
of ciliates is performed with the 10× objective.
The microscopic field
The complete preparation is examined, leav-
The microscopic field is the circular image one ing no parts missed out. To accomplish this,
sees at a certain magnification. one should work systematically (Figure 2.49).
The microscopic field is divided according to Always start at a corner of the coverslip, for
the plate of a clock. Doing so, we can locate any example, the upper-left corner and proceed by
object in this microscopic field, starting from the looking at the next microscopic field, with a
centre (see Figure 2.48): small overlap. This means that each time when
a field has been examined, an object in this field,
• between one and two o’clock we can see a for example, a crystal, at three o’clock is chosen,
thrombocyte between two red blood cells and is brought towards nine o’clock. This sec-
• the object near two o’clock is a neutrophil ond field is examined and so on. In this way, one
• the object between four and five o’clock is a should go in a straight line from the upper-left
monocyte corner towards the upper-right corner from the
• between the centre and ten o’clock we can see coverslip. Once we arrive there, we choose an
a lymphocyte object at six o’clock and move it towards twelve
• at the edge, near eight o’clock, we can see o’clock. This results in arriving at the row below
part of a lymphocyte. the one that has just been examined (again with
a small overlap). This time we work from right to
left. This way the complete preparation should
be examined within the edges of the coverslip,
until arriving at the lower-right corner.

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