Clinical and laboratory observations indicate that the antibacterial activity of the new antibiotic, tetracycline, closely resembles and in most respects is almost identical with that of oxytetracycline (Terramycin) and chlortetracycline (Aureomycin).1 Therapeutic effectiveness of systemically administered tetracycline hydrochloride has, to date, been distinguished by an unusually high degree of toleration and reportedly no serious toxic reactions of either a local or a systemic character.*