Page 238 - Zoo Animal Learning and Training

222 Tasks for the Veterinary Assistant

by pushing the stop button or turning the timer
to zero.
3. Never try to stop or slow down a rotating centrifuge
with your hand. If you suddenly stop a centrifuge it
can remix your sample. Another issue with stopping
it by your hand is it’s an accident waiting to happen!
You can lose a finger or severely burn your fingers
by friction. Wait the two minutes it takes for the
centrifuge to stop fully.
4. Wipe up any fluids that may have spilled in the
centrifuge. Spilled fluids will off balance your
centrifuge. If you pull out a test tube that isn’t as full
as it was when it went in check the tube for fluid.
Plastic test tubes are notorious for developing cracks
and spilling their contents into the centrifuge tube.
Use disinfectant and paper towels twisted enough to
reach to the bottom of the tube. Take extra care if
the test tubes are glass as they shatter into tiny little
pieces that are difficult to remove from a finger!
Practices will often have at least two centrifuges: one
for small micro‐hematocrit tubes and a standard‐sized
centrifuge with variable speeds (rpm), a timer, and dif-
ferent‐sized centrifuge tubes to accommodate different‐
sized test tubes. The larger centrifuges can be either
fixed slant or swinging bucket heads. Some centrifuges
have interchangeable heads, with the heads changed
depending on the sample to be run. Whatever the type FIGURE 12.2 Refractometer.
blood, urine and feces are placed in test tubes and spun
in a centrifuge for their various components. By keeping read 1.000, which is the specific gravity of water. The
them clean and maintaining them as per the owner’s smaller scale to the right or left of the large scale is to
manual you will be of great value to the team. measure total protein. Don’t worry about that number. If
the specific gravity scale is off, find the little screw on the
Learning Exercise refractometer, usually close to the eyepiece and turn it
one way to bring the line to 1.000.
Take a look at the school’s or your workplace’s If the refractometer is not properly calibrated, invalid
centrifuges. Practice balancing and then running results may occur. Record who did the calibration and
them with water in the tubes. when it was done in the maintenance log.

Refractometer Learning Exercise

Put a drop of distilled water on the lens of the
A refractometer (Figure 12.2) is used to determine urine refractometer, hold it up to the light and find
specific gravity, which is an indication of kidney function where the line is to indicate the specific gravity of
and to measure total protein in plasma, which can indi- the water.
cate inflammation. Each of these has on its own scale on
the refractometer. Refractometry is light passing through
a liquid and refracted by dissolved substances in the
liquid. Upkeep on the refractometer is easy. Clean it with Sample Collection
water from the tap and use a lens paper to wipe the lid
and the glass surface dry. The only other maintenance Every sample tested must be prepared according to the
required is to check its calibration once a month. Place a directions for testing as per the piece of equipment required
drop of distilled water on the glass surface and gently to run the test or if it’s a manual test. This often includes:
put the lid over the drop. Hold the refractometer to your
eye and under a light source. The ceiling light should be 1. Accurate volume or weight measurements. Too little
sufficient. The line on the specific gravity scale should or too much sample will skew results.