Biological field and laboratory methods for measuring the quality of ...

float, examine the underside of the cover slip and
add these organisms to the total count. Lower
the objective lens carefully into position with
the coarse focus adjustment to ensure that the
cover slip will not be broken. Fine focus should
always be up from the cover slip.
When making the strip count, examine two to
four "strips" the length of the cell, depending
upon the density of organisms. Enumerate all
forms that are totally or partially covered by the
image of the Whipple grid.
When making the field count, examine a
minimum of 10 random Whipple fields in at
least two identically prepared S-R cells. Be sure
to adopt a consistent system of counting organisms
that lie only partially within the grid or
that touch one of the edges.
To calculate the concentration of organisms
with the S-R cell, for the strip count:
ex 1000 mm 3
No. per m! = L X D X W X S
where:
C = number of organisms counted (tally)
L = length of each strip (S-R cell length), mm
0= depth of a strip (S-R cell depth), mm
W= width of a strip (Whipple grid image
width), mm
S = number of strips counted
To calculate the concentration of organisms
with the field count:
ex 1000 mm 3
No. per m! = A X D X F
where:
C = actual count of organisms (tally)
A = area of a field (Whipple grid image area),
mm 2
0= depth of a field (S-R cell depth), mm
F = number of fields counted
Multiply or divide the number of cells per
milliliter by a correction factor for dilution
(including that resulting from the preservative)
or for concentration.
9
PLANKTON COUNTING
Palmer-Maloney (P-M) Nannoplankton Cell
The P-M cell was especially designed for
enumerating nannoplankton with a high-dry
objective (45 X). It has a circular chamber 17.9
mm in diameter and 0.4 mm deep, with a
volume of 0.1 ml. Although useful for examining
samples containing a high percentage of
nannoplankton, more counts may be required to
obtain a valid estimate of the larger, but less
numerous, organisms present. Do not use this
cell for routine counting unless the samples have
high counts.
Pipet an aliquot of well-mixed sample into
one of the 2 X 5 mm channels on either side of
the circular chamber with the cover slip in place.
After 10 minutes, examine the sample under the
high-dry objective and count at least 20 Whipple
fields.
To calculate the concentration of organisms:
ex 1000 mm 3
No. per m! = A X D X r
where:
C = number of organisms counted (tally)
A = area of a field (Whipple grid image), mm 2
o = depth of a field (P-M cell depth), mm
F = number of fields counted
Bacterial Counting Cells and Hemocytometers
The counting cells in this group are preciselymachined
glass slides with a finely ruled grid on
a counting plate and specially-fitted ground
cover slip. The counting plate proper is separated
from the cover slip mounts by parallel
trenches on opposite sides. The grid is ruled such
that squares as small as 1/20 mm (50 IJ.) to a side
are formed within a larger l-mm square. With
the cover slip in place, the depth in a Petroff­
Hausser cell is 1/50 mm (20IJ.) and in the
hemocytometer I/l 0 mm (lOOM). An optical
micrometer is not used.
With a pipet or medicine dropper. introduce a
sample to the cell and at high magnification
identify and count all the forms that fall within
the gridded area of the cell.
To calculate the number of organisms per
milliliter, multiply all the organisms found in the
gridded area of the cell by the appropriate
factor. For example, the multiplication factor