Counting cells with a haemocytometer
Appendix 10
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A haemocytometer is a specialized
microscope slide used to count cells,
organelles, etc. It has a thick base and uses a
special coverglass which is thick enough to
stay flat under the pull of surface tension
from the solution in the counting chamber.
To load: Assemble the haemocytometer.
Inject ~15 µl of solution per side, using the
loading notch. Make sure that the chamber is
fully loaded with liquid, plus some excess in
the channels beside it.
The centre portion of the slide has etched grids with precisely spaced lines. The coverslip is
positioned 100 µm above the slide.
The shaded square (left) has sides of
200 µm x 200 µm, bounded by three
lines. The centre line marks the 200
µm spacing. The volume over the
shaded square is 200 x 200 x 100
µm3, or 4 x 106 µm3. 1 µl = 1 mm3 =
109µm3. The volume over the
200µm square is 4 x 10-3 µl, which
is one 250th of a µl
The smallest square has sides 50 µm
x 50 µm. The volume over the
smallest square is 2.5 x 104 µm3,
which is 2.5 x 10-4 µl, which is one
4000th of a µl.
To count Aspergillus spores: make a
1:100 dilution of a harvested culture. Count the number of spores in 10, 200 µm squares (five per
side), and average. Calculate the number of spores per µl as
(average per 200µm square) x 250 x 100 (dilution factor, which can vary as needed)