PREFACE 



III any altcnij)! lo classity and dixidc li\- 

 in^ systems, nay, cvcmi li\ini>; rrrsus non- 

 luing systems, certain hoiderline bodies are 

 encountered which ma>' he considered as 

 transition forms from ont* j2;r()up to another. 

 This was recojj;nized l)y tiie eai"ly students 

 of the microscopic forms of life, wiio con- 

 sidered the bacteria and similar orji;anisms 

 as "protista" or primiti\-e bodies, i-elatcd, on 

 the one hand, to the i)lants and, on the 

 other hand, to animals. Recently accumu- 

 lated information points also to viruses as 

 transitory between nonliving and living 

 bodies. 



The actinomj^cetes form sucli a l)orderline 

 system, but on a much more speciahzed 

 scale. Considered by some as bacteria 

 ("higher bacteria"), or Eubacteriales, and 

 bj' others as fungi ("lower fungi"), or 

 Hyphomyeetes, actinomycetes are often 

 placed in a group by themselves, with some 

 of the properties of both. There are found, 

 among the actinomycetes, certain forms 

 that are more closely related to the bacteria 

 and others that are nearer to the fungi. 



M}^ personal attention was first directed 

 to the actinomycetes about 45 years ago. In 

 1914, as a senior in college, specializing in 

 soil microbiology, or, as it was designated 

 at that time, "soil bacteriology," I was as- 

 signed b}' my professor, Jacob G. Lipman, 

 the task of making a comparati\-e monthly 

 study of the bacterial population of certain 

 soil types located on the experimental 

 grounds of the college. The results obtained 

 in this study were used for a thesis which I 

 presented the following June for my B.Sc. 

 degree.* 



Throughout the year 1 9 1 4- 1 9 1 o , I sampled , 



* "Bacteria, Actinomyces and Fungi in the Soil." 

 Selman A. Waksman, Thesis, Rutgers College, New 

 Brunswick, X.J., 1915 (Abstract published in J. 

 Bacteriol. 1: 101, 1916). 



at monthly in(er\ais, se\-erai dilTerent .soil 

 types. Sami)les taken undei- sterile condi- 

 tions were obtainetl from \arious depths 

 (fiom the surface to 30 inches). These I 

 brought to the laboratory and plated out, 

 using suital)le dilutions and proper culture 

 media. After \arving periods of incubation, 

 I counted the colonies of bacteria developing 

 on the plates. I was soon struck \}y the fact 

 that a fairly large number of the colonies 

 that 1 could ob.serve did not look exactly 

 like the majority of the others, more typical 

 of bacteria. These particular colonies were 

 compact and leathery in nature, pyramidal 

 in structure, penetrating deep into the agar 

 medium, freciuently covered with a surface 

 fuzz that W'as distinct from the substrate 

 growth. On examination of such colonies 

 even with a low-power microscope, the fuzzy 

 growth proved to be made up of an aerial, 

 branching mycelium that resembled that of 

 fungus colonies. 



When I brought the plates to my professor, 

 he shook his head, smiled, and said, "Yes, I 

 have been aware of the occurrence of these 

 types of bacteria. Freciuently they are desig- 

 nated as a special group, under the name 

 actinomyces. You had better go and see our 

 botanist. Professor M. T. Cook. He may be 

 able to tell you more about them." Professor 

 Cook was indeed familiar wdth the group, 

 but merely as causative agents of potato 

 scab. He considered them, not as bacteria 

 but as fungi. He referred me to various 

 papei's in which further information could 

 be obtained on this group of organisms. I 

 decided in my ^•ery early studies, that the 

 organisms could be differentiated from both 

 bacteria and fungi. To my great satisfaction, 

 I learned later that similar suggestions had 

 already been made previously by others. 



Thus, at the \-ery threshold of my scien- 



