A rapid procedure for leukoagglutination by specific antisera and conditions which influence it are presented. The procedure consists in suspending leukocytes in a small volume of saline, counting the cells with pipette and chamber and measuring out 27,000 cells per mm3 in 0.05 ml of normal saline. To the cells is added 0.5 ml of antiserum diluted with normal saline. The cell-antiserum mixture is centrifuged for one minute and the results are read. The entire procedure is carried out at 22 to 26 C.

Agglutination of leukocytes is inhibited at 8 C and the velocity is reduced at 37 C. The optimal temperature is 22 to 26 C. Centrifuging results in the greatest speed of antigen-antibody reaction. Immature leukocytes and especially those outside the body for 2 to 3 days are destroyed more readily than mature cells by hypotonic salt solution. Agglutination requires the presence of intact cells. Electrolytes are necessary for the visible phase of agglutination and the optimal range is 0.85 to 2.5 per cent. Mature leukocytes are agglutinated in lower concentrations. Ageing of cells outside the body interferes with agglutination and mature leukocytes are agglutinated up to the fourteenth day. Immature cells show little or no clumping after the fourth day. Repeated washing of leukocytes does not interfere with agglutination until after the tenth time when most of the cells are destroyed. Hemoglobin up to 50 per cent does not interfere with agglutination. A definite number of leukocytes is necessary for a satisfactory agglutination. Excess or decrease in the number of cells modifies the degree of clumping.

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