THE LEUKOCYTES

Although the leukocytes have been recognized since the days of Hewson as constituents of the blood, and their importance in pathologic processes was forecast by Virchow, it must be freely admitted that many features of their origin and function remain to be elucidated. To the clinician who is accustomed to estimate the number of white cells in blood specimens as a matter of routine and to make deductions of diagnostic and prognostic import from his observations, this confession of ignorance may seem unwarranted. Yet even the most readily secured data—those of the leukocyte count—present variations in admittedly healthy persons that are not yet easily explained. One often hears that the average normal total leukocyte count is 7,500 per cubic millimeter; nevertheless, the more recent investigators seem to agree in the advice that it is the normal range rather than the average number of the blood cells that should be sought.