RECOGNITION OF ANTIBIOTICS 



19 



trichomycin (1952), candidin (1954), and 

 amphotericin B (1955). Others have been 

 found which ha^'e pronounced antitumor 

 action; these include, apart from the actino- 

 mycins, azaserine (1954), .sarkomycin (1953), 

 carzinophilin (1954), 6-diazo-5-oxo-L-norleu- 

 cine (DON) (1956), and mitomycin (1956). 

 New antibiotics are still being discovered; 

 most of them are being isolated from cultures 

 of actinomycetes. Some are still being 

 introduced into medical practice. As yet, 

 however, no useful anti\'iral antibiotics have 

 been isolated. 



The uses of antibiotics have been extended 

 far beyond their original chemotherapeutic 

 provinces, and e\'en into the fields of animal 

 feeding and food preservation. Some anti- 

 biotics are used by the geneticist to select 

 mutants of bacteria; here streptomycin oc- 

 cupies a place of choice. Others are used by 

 the biochemist as specific inhibitors of 

 metabolic reactions, such as chloramphenicol 

 (inhibition of protein synthesis) and anti- 

 mycin A (inhibition of cj'tochrome oxidase). 

 The marvelous potentialities of the anti- 

 biotics have not vet been exhausted. 



