Haemocytometer cell counts and dilutions

Overview

Recall questions on the ruling and 0.1 mm depth of the haemocytometer, volumes over its squares, loading it until Newton's rings appear, diluting blood and the boundary-line rule, calculating dilution factors and erythrocyte and leucocyte counts, recognising anaemia, and sources of counting error.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a haemocytometer?

   Model answer

   It is a thick glass slide with a counting grid of known dimensions etched into a central platform that sits a precise, known depth below the coverslip, so that a known volume of cell suspension lies over each square.

2. 2

   What is the depth of the counting chamber of a haemocytometer?

   Model answer

   0.1 mm.

3. 3

   How is the central square of an improved Neubauer haemocytometer ruled?

   Model answer

   The central square measures 1 mm by 1 mm and is divided into 25 large squares each 0.2 mm by 0.2 mm, and each of those is further divided into 16 small squares.

4. 4

   Calculate the volume of suspension lying over one of the 25 large squares of the central grid.

   Model answer

   0.2 mm × 0.2 mm × 0.1 mm = 0.004 mm³.

5. 5

   Calculate the volume of suspension lying over the whole 1 mm by 1 mm central grid.

   Model answer

   1 mm × 1 mm × 0.1 mm = 0.1 mm³.

6. 6

   Describe how a haemocytometer is loaded with a cell suspension.

   Model answer

   The coverslip is moistened and pressed firmly onto the supports until Newton's rings appear, then a small drop of well-mixed suspension is touched to the edge of the coverslip and drawn under the chamber by capillary action, with no bubbles and no overflow into the moat.

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