Abstract
Dog leukocytes bind a specific type of y-globulin in situ. This is identical with fraction IV of serum [gamma]-globulin isolated by cellulose phosphate chromatog-raphy. This fraction stimulates phagocytosis in vitro to levels comparable to that obtained for complement-inactivated normal serum. A medium of low ionic strength is described that is considerably more suitable for this type of investigation on phagocytosis than Hank''s medium.