Hemocytometer

The hemocytometer (or haemocytometer, or Burker's chamber) is a counting-chamber device originally designed and usually used for counting blood cells.

[1] The hemocytometer was invented by Louis-Charles Malassez and consists of a thick glass microscope slide with a rectangular indentation that creates a precision volume chamber.

The device is carefully crafted so that the area bounded by the lines is known, and the depth of the chamber is also known.

Petroff-Hausser counter using Improved Neubauer rulings is used for bacteria or sperm counts, and is offered with varying chamber depths.

The Sedgwick-Rafter Cell ruling in a hemocytometer is primarily designed for use in the microscopy of drinking water.

The gridded area of the Improved Neubauer ruled hemocytometer consists of nine 1 x 1 mm (1 mm2) squares.

The raised edges of the hemocytometer hold the coverslip 0.1 mm off the marked grid, giving each square a defined volume (see figure on the right).

When the two glass surfaces are in proper contact Newton's rings can be observed.

If so, the cell suspension is applied to the edge of the coverslip to be sucked into the void by capillary action which completely fills the chamber with the sample.

The volume of the squares counted is the one shown in the table at the top, depending on the size (see figure on the right).

This ensures the sample is representative, and not just an artifact of the particular region of the original mixture it was drawn from.

If it is too dilute, the sample size will not be enough to make strong inferences about the concentration in the original mixture.

Sedimentation is less of a problem with bacteria but evaporation, more prevalent in low-humidity air-conditioned laboratories, still has to be minimized.