AUTOMATIC APPARATUS FOR DETERMINING THE PERCENTAGE POPULATION OF PARTICULATES IN A MEDIUM

New and improved automatic method and apparatus for differentiating and determining the respective populations of specific particulates in a medium, for example, leukocytes in a whole blood sample comprises means for treating a number of phased quotient streams, each containing a portion of such blood sample, so as to stain either a specific type or a specific class of leukocytes, and passing each quotient stream through a corresponding viewing chamber. The number of stained leukocytes to the number of both stained and unstained leukocytes in each sample portion passing through the corresponding viewing chamber are counted concurrently by photometric means, the ratio of such numbers indicating the population of such specific leukocytes or such specific class of leukocytes in the corresponding sample portion. Preferably, the counting of both stained and unstained leukocytes in the sample portions in the different quotient streams are counted to a same predetermined reference, whereby the respective populations of the specific types or specific classes of leukocytes are directly related and recorded in correlated fashion, and any variations in either the flow rate or the volume of the sample portions in the different quotient streams are only incidental. Also, when particular leukocytes of a same quotient stream are stained and counted as a class, comparison-type logical operations determine the respective populations of the individual leukocytes in such class.