320 OUTLOOK FOR THE FUTURE 



bacteria, its toxicity to animals, and its activity in vivo. The following 

 illustrations will suffice: 



Of all the aerobic spore-forming bacteria known to produce anti- 

 biotic substances, only B. brevis and B. subtilis have been utilized for 

 the isolation of tyrothricin, bacitracin, and subtilin. It is known, for 

 example, that various strains of B. niesentericuSy B. mycoideSy B. sim- 

 fleXy and other spore-forming bacteria are capable of producing anti- 

 biotics, some of which are markedly different chemically, biologically, 

 or in selective activity. It is sufficient to call attention to such prepara- 

 tions as bacillin, simplexin, and others. A more detailed study of these 

 organisms and the substances produced by them is bound to enlarge 

 greatly our knowledge of this group of chemical compounds and their 

 therapeutic potentialities. 



Of all the nonspore-forming bacteria possessing antagonistic prop- 

 erties found in soils and water basins, only two have been studied in de- 

 tail : Ps. aeruginosa has been utilized for the production of pyocyanase, 

 pyocyanin, and the various pyo-compounds, and Ch. iodinum for the 

 production of iodinin. It is known, however, that a large number of 

 other nonspore-forming bacteria are capable of producing a variety of 

 antibiotic substances, the chemical nature and biological activities of 

 which are still but little understood. 



Only very few of the antibiotic substances produced by actinomycetes 

 have so far been investigated, isolated, or concentrated; namely, acti- 

 nomycin, proactinomycin, streptothricin, and streptomycin. Even these 

 few substances, however, differ markedly in chemical nature and in 

 biological activity. In view of the fact that as many as 20 to 40 per cent 

 of all the actinomycetes are known to be capable of producing antibiotic 

 substances, many of which undoubtedly differ from those already iso- 

 lated, the wealth of material that is awaiting investigation can only be 

 surmised. Some of these possibilities have been definitely indicated. 



The production of antibiotic agents by fungi likewise has been but 

 insufficiently studied. The following pertinent facts may direct attention 

 to the many problems still awaiting investigation : 



(a) Some antibiotics, like penicillin, gliotoxin, clavacin, aspergillic acid, 

 penicillic acid, and citrinin, are produced by a number of different 



