Numerous organisms have been examined in our laboratories to determine their antibiotic potentialities. Among those that were selected for more intensive study was a soil actinomycete that had been isolated and found to possess antibacterial activity in Dr. Burkholder's1 laboratory. On Moyer's sporulation agar, the organism produces a spreading, slightly wrinkled thallus. Aerial mycelium is white until covered with pale tan-gray spores. Oblong to oval spores are formed in unbranched, slightly

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... rved chains on simple or dichotomously branched aerial hyphal tips. Abundant sporulation occurs at room temperature; little or none occurs at 37 C. The organism, which is evidently a Streptomyces, will be described more fully elsewhere. This organism produces an antibiotic substance that is different chemically from any thus far described. The antibiotic has been isolated in crystalline form and has been found to contain both nitrogen and nonionic chlorine. The proposed name for this antibiotic is "chloromycetin" (Ehrlich et al., 1947). Recently Carter, Gottlieb, and Anderson (1948) announced the independent isolation of this substance from culture filtrates of a Streptomyces obtained from central Illinois. This paper describes some antibiotic properties of culture filtrates and crystalline material, microbiological assay methods, the cultural conditions employed, and some toxicity and chemotherapy data for the crystalline chloromycetin. ANTIBIOTIC ACTIVITY OF THE STREPTOMYCES Agar cultures. This organism in company with many others was first tested against various bacteria and fungi on agar. The Streptomyces was streaked across the center of agar plates and allowed to grow for 4 days at 28 C. Several different agar media were employed. After this incubation period the test bacteria were streaked at right angles to the Streptomyces and were incubated for an additional 48 hours at 37 C. Similar plates were cross-streaked with test fungi and incubated for an additional 7 days at 28 C. At the end of these incubation periods the zones of inhibition of the test organism were measured in millimeters. Table 1 gives the results of such tests. The data in table 1 indicated that the organism produced on several solid media a substance or substances inactive against the yeasts and filamentous fungi tested but active against certain gram-negative, gram-positive, and acidfast bacteria. It was also noted that although the character of the nitrogenous