Instrument used for this purpose is improved Neubauer Haemocytometer. The instrument consist of (1) a special glass slide (counting chamber), (2) one graduated pipette for RBC count. 1 drop of diluted blood from the red cell - counting pipette is introduced in the counting chamber under the cover slip. Since the under surface of the cover-slip is l/10th mm high from the surface of the counting chamber, the volume of each small square is 1/4,000th cu. mm. Red blood cells are counted in the five groups of 16 small squres. To avoid counting a corpuscle twice, those on a line are counted only when on the top and left lines or on the bottom and right lines