Abstract
1. Mononuclear phagocytes of immunized animals that had ingested tubercle bacilli in vivo and had subsequently been transplanted and grown in the environment of a normal animal continue to inhibit the multiplication of the microorganism in their cytoplasm in the absence of immune body fluids. 2. Mononuclear phagocytes of immunized animals that had ingested tubercle bacilli in vitro in the presence of immune serum inhibit the multiplication of the microorganism in their cytoplasm to a much greater extent than cells of normal animals that had ingested the bacteria in the same medium and had grown in a similar environment. 3. The presence of immune serum during the in vitro ingestion of tubercle bacilli by mononuclear phagocytes of normal animals does not regularly endow them with increased bacteriostatic properties for the microorganism. Whether or not continued sojourn of normal cells in immune body fluids will confer upon them such properties has not been determined. 4. Mononuclear phagocytes of immunized animals that had ingested tubercle bacilli in vitro in a medium of normal serum and had subsequently grown in an environment devoid of immune body fluids inhibit the multiplication of the microorganism in their cytoplasm to a much greater extent than do normal cells under the same conditions. 5. Active tuberculosis confers on the mononuclear phagocytes themselves increased bacteriostatic properties for the tubercle bacillus which are independent of the immune body fluids or of the organ environment in which they grow.