INTRODUCTORY 



\() otluM" ;j;r()up of luicrolx-s, niid lor thai 

 matter no other iiroup ot li\iii!^ systems, 

 whether ol' |)laiit, animal, or miei'ohial ori<;iii, 

 lias been in recent yeai's the t'oeus of so much 

 attention In' the invest ij^ator, especially the 

 microbiologist, the chemist, and the medical 

 scientist, and hy the pharmaceutical manu- 

 facturer, as the actinomycetes. Only 20 

 years ago scarcely a dozen laboratories in 

 the whole world were de\-oting much atten- 

 tion to this group of organisms, and they 

 were concerned largely with either disease- 

 producing or soil-inhabiting forms. Today, 

 literally thousands of investigators in numer- 

 ous laboratories throughout the world are 

 isolating cultures of actinomycetes from 

 soils and other substrates and studying 

 their physiological and biochemical activi- 

 ties. This increased attention is due primaril}' 

 to the discovery that the actinomycetes 

 comprise many forms that ha\'e the capacity 

 to produce a large number of chemical sub- 

 stances capable of inhibiting the growth of 

 microorganisms, especially disease-producing 

 forms. These substances have come to be 

 known as antibiotics. The discovery that 

 certain actinomycetes can produce growth- 

 promoting substances or vitamins and cer- 

 tain potent enzyme systems has added 

 greatly to this interest. ]\Iany of the anti- 

 biotics produced by the actinomycetes have 

 found extensive practical application in the 

 control of infectious diseases of man, ani- 

 mals, and plants; also in animal nutrition; 

 and in the preservation of biological prod- 

 ucts, including virus preparations, and of 

 human foodstuffs. 



Our first knowledge of the actinomycetes 

 dates back to 1875, when l-crdinand Cohn 

 named an organism he found in the tear duct 

 of the human eye Streptothrix Foersteri. This 

 was soon followed (1877 to 1878) by a de- 



scription by Ilarz, of another organism, 

 Artinotni/ccs hoiis, found in "lumpy jaw" of 

 cattle. Since I hen, many act inomycetes have 

 been isolated, and a niunber of genera and 

 hundreds of species have been described. 

 These include organisms causing animal and 

 plant diseases and numerous saprophytes 

 occurring in soils, in dust, in water basins, 

 and in other natural substrates. 



Because of the above two generic names 

 and for other reasons, the systematic posi- 

 tion of actinomycetes became highly con- 

 fused. Animal and plant pathologists, bota- 

 nists, zoologists, mycologists, bacteriologists, 

 and biochemists were eager to introduce new 

 names in describing as new species freshly 

 isolated cultures of actinomycetes. New 

 genera and new species were thus created, 

 without due regard to previously established 

 names or even previous descriptions. This 

 tended to complicate greatly our knowledge 

 of the taxonomy and classification of the 

 actinomycetes. 



A number of subsequent milestones in the 

 history of actinomycetes should be noted. 

 Among them were the isolation by Israel of 

 a pure culture of an anaerobic organism, for 

 which the generic name Actinomyces was re- 

 served; the introduction of synthetic media 

 by Krainsky and by Waksman and Curtis; 

 the recognition of the sporulating mecha- 

 nisms of actinomycetes by 0rskov; the clas- 

 sification systems of Waksman and Henrici 

 and of Krassilniko\' ; the isolation of anti- 

 biotics from cultures of actinomycetes; and 

 finally the studj^ of the cell walls of actino- 

 mj'cetes. These and numerous other mile- 

 stones have marked the development of our 

 knowledge of the actinomycetes from the 

 original concept that they were a small group 

 of negligible organisms causing certain ob- 

 scure diseases to the comprehensive recog- 



