In Retrospect 



Since the discovery of the great potentialities of antibiotics as cbemo- 

 therapeutic agents, interest in the actinomycetes has greatly increased. 

 Following the rediscovery of penicillin, the most important antibiotics dis- 

 covered during the past 10 years and utilized in the treatment of human, 

 animal and even certain plant diseases, as well as in the nutrition of non- 

 herbivorous animals, are produced by actinomycetes. At least ten such 

 compounds are now being used clinically on a large scale. Several others 

 are on their way. 



Most of the antibiotics so far isolated are active largely upon bacteria 

 and actinomycetes; some are active upon fungi, a few upon protozoa or 

 viruses. Our knowledge of anti-tumor properties of antibiotics of actino- 

 mycetes is still very limited; there is no doubt, however, that such sub- 

 stances exist, as in the case of the cytostatic action of some of the prepara- 

 tions; how soon they may become effective as chemotherapeutic agents 

 still remains to be determined. We know already that just as the antibac- 

 terial and antifungal substances are characterized primarily by their specific 

 spectra or range of activity upon different organisms, so are the true anti- 

 viral and anti-tumor agents. 



An attempt has been made in the guide to bring together the descrip- 

 tions of the various well-authenticated cultures of actinomycetes, so as to 

 aid in their identification, as well as to summarize the information of the 

 antibiotics produced by them, without any exhaustive treatment of either 

 of these two phases of our knowledge of actinomycetes and their biochemical 

 potentialities. 



Many species of actinomycetes listed in the literature have so far been 

 only incompletely described. A line had to be drawn, however, between a 

 complete or exhaustive description of a species and an extremely poor or 

 insufficient description. In selecting the cultures for inclusion in this guide, 

 consideration has been given to the significance of the substrate from which 

 they were isolated, their particular morphology, their important physiolog- 

 ical properties or their ability to produce specific antibiotics. 



Although an attempt has been made to include all the antibiotics pro- 

 duced by actinomycetes, certain limitations have been encountered here as 

 well. Many of the preparations are only incompletely described. Some are 

 no doubt synonyms, but they cannot be recognized at this time. Many 

 preparations have been referred to in the scientific literature or in the press, 

 but their descriptions have not become available to the authors at the time 

 of writing. It is known, for example, that several antibiotics have been 



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