“…The various tetracyclines have been the subject of thorough investigations regarding their chemical and physical as well as pharmacological properties (Regna et al 1951, Stephens et al 1952, Boothe et al 1953, Cunningham et al 1953, Conover et al 1953, Dowling 1955, Regna 1955, Lepper 1956, Musselman 1956, Kunin et al 1959, Kunin and Finland 1961, Spitzy 1962.…”