Hemacytometer counting chamber (WBCs). Areas marked A, B, C,
and D are used to count white blood cells.
(1) Routinely, blood is drawn to the 0.5 mark and diluted to the 11 mark with
WBC diluting fluid. All the blood is washed into the bulb of the pipet (which has a
volume of 10). Therefore, 0.5 volumes of blood are contained in 10 volumes of diluting
fluid. The resulting dilution is 1:20. (These figures are arbitrary and refer strictly to
dilution and not to specific volumetric measurements.)
(2) The depth of the counting chamber is 0.1 mm and the area counted is 4
sq mm (4 squares are counted, each with an area of 1.0 sq mm therefore, 4 X 1.0 sq
mm = a total of 4 sq mm). The volume counted is: area X depth = volume. Four sq
mm X 0.1 mm = 0.4 cu mm.