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In a recent case of splenomyelogenous leukemia in which the leukocytes approached 350,000 per c.mm. the great abundance of white cells in the stained spread made an accurate differential count almost impossible. After some delay, however, the task was easily and accurately carried out by cutting a square from the end of a microscopic slide of just the exact size to fit within the eyepiece and rest on its diaphragm.
With a glazier's diamond, and by most delicate pressure, four lines were ruled parallel with each side of the square and forming a small square in its center. This, when placed in the eyepiece, the lines being down, gave the outline of a small square on the stained spread and within the usual round field and permitted the easy and accurate counting and classification of cells within its borders, the slide being moved to include a new lot in proximity
Sheaff PA. A SIMPLE AND PRECISE METHOD OF DIFFERENTIAL LEUKOCYTE COUNTING WHERE THE WHITE CELLS ARE GREATLY INCREASED. JAMA. 1912;LVIII(25):1941. doi:10.1001/jama.1912.04260060290013
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