Chloramphenicol is an antibiotic which initially was isolated from culture filtrates of the fungus Streptomyces venezuelae (1-3) by Bartz (4) and subsequently was synthesized chemically (5-7).Chloramphenicol ( Material for this study consisted of crystalline chloramphenicol obtained from culture filtrates, and the synthetic product.Chloramphenicol was administered intravenously in aqueous propylene glycol or acetamide solutions to small animals at a rate of 0.1 cc. per ten seconds; dogs received 1.0 to 3.0 cc./min. Acute toxicity results are based on a seven-to 14-day observation period and chronic tolerance studies were carried out for two to four weeks in small animals and for periods of three and five weeks and over four months in dogs. The Dragstedt et al. (8) method served to interpolate results.

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 curved 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 ' Early lots were prepared by Quentin R. Bartz; later lots, by Clark E. Cottrell.

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