haemocytometer A device used to estimate the concentration of cells in blood samples. Typically a haemocytometer consists of a glass slide with a shallow depression divided into a fine-meshed grid; each of the grid compartments is about 0.05 mm square. The slide is placed under a microscope and the number of cells in each square of the grid can be counted, which enables the concentration of blood cells in the sample to be assessed. Haemocytometers are also used in estimating the number of microorganisms present in a sample of water or other fluid.

haemocytometer (hee-moh-sy-tom-it-er) n. a special glass chamber of known volume into which diluted blood is introduced. The numbers of the various blood cells present are then counted visually, through a microscope.