a special, standardized glass slide used for counting cells (especially erythrocytes and leukocytes) and other particulate material in a measured volume of fluid; the central portion is precisely ground in such a manner that the uniformly flat surface is exactly 0.1 mm lower than that of two parallel ridges on which a special, uniformly flat coverslip may be placed; accurately etched lines on the flat central portion form the boundaries of groups of squares of known areas, thereby providing the basis for determining the volume of fluid in which the cells are counted. Glass slides of this type are frequently known as hemocytometers.