PREFACE 



Three and a half decades ago— in the spring of 1914— the u^iter, 

 then a senior at Rutgers College, dug a spade into the earth of the New 

 Jersey Agricidtnral Station experimental plots, to study the distribution 

 of different groups of microorganisvis occurring at different depths in 

 the soil. This operation was repeated monthly, and sterile soil samples 

 were remolded to the laboratory and examined by use of ordinary plat- 

 ing procedures. A relatively simple agar medium was used. 



Among the soil organisms that attracted the particrdar attention of 

 the yotithful investigator were the actinomycetes. Althotigh he also 

 enumerated the bacteria and the filamentous fungi, he was struck pri- 

 marily by this much-neglected group of soil inhabitants, frequently 

 spoken of as ray fungi and said to belong to the genus Actinomyces or 

 Streptothrix. On December 28, 1915, he presented before the 17th 

 Annual Meeting of the Society of American Bacteriologists, a paper on 

 the subject of "Bacteria, actinomyces and fungi in the soil." In this, 

 his first contribution to the knowledge of the microbiological population 

 of the soil, he said: 



"The actinomyces grow very slowly; they begin to develop from the 

 bottom of the plate, and to the casual observer the colonies formed look 

 like those of bacteria, even after 5-6 days' incubation; only the some- 

 what mealy or roiigh surface will disclose the fact that they are not 

 bacteria. It requires carefid observation to tell whether those white, 

 pink or grey colonies are bacteria or not. Many cotmts of bacteria 

 might have been confused, when this point was not known, and the 

 fungi and actinomycetes were not taken into consideration." 



Since this early survey of the occiirrence and abundance of actino- 

 mycetes at different soil depths and in different soil types, the ivriter 

 and his mimerous associates and students have devoted much time to 

 the study of the actinomycetes, their cidtural characteristics, recognition 

 of type species, their classification, their physiological properties and 

 biochemical activities, their importance in the decomposition of pure 

 organic compounds as well as of complex plant atid animal residues in 

 soils, peats, and composts, and finally their ability to produce antibiotic 

 substances. 



The writer has thus been concerned, d^iring virtually his entire sci- 

 entific lifetime, with the study of the actinomycetes. In summarizing 

 our present knowledge of this interesting and important group of micro- 

 organisms, he has attempted to assemble the work of other investigators, 

 ivith somewhat greater emphasis upon the work done in the laboratories 



