10 



THE ACTIXOMYCETES, Vol. I 



where they may exceed in numbers other 

 groups of microorganisms; this was explained 

 by their greater resistance to conditions 

 unfavorable to their nutrition. Beijerinck 

 thus laid the groundwork for our present 

 knowledge of the occurrence and physiol- 

 ogy of actinomycetes. He also believed that 

 these organisms play an important role in 

 the humification of the organic matter in soil. 

 Among the other fundamental studies on 

 the actinomycetes carried out during the 

 early days of this period, mention should be 

 made of the work of Hiltner and Stormer, 

 who made the first comprehensi\'e study of 

 the abundance of actinomycetes in the soil. 

 They found that the season of year and soil 

 treatment have a great influence upon the 

 numbers of these organisms. This work was 

 soon followed by that of numerous other in- 

 vestigators, notably that of Fisher (1909), 

 Fousek (1913), H. J. Conn (1913-1918), 

 Krainsky (1914), and Waksman and Curtis 

 (1916, 1918). The role of actinomycetes in 

 the breakdown of organic residues in the soil, 

 methods for determining their presence and 

 abundance in the soil, and the recognition of 



Ficu;re 7. Growth of an actinomycote in a 

 compost, as shown by contact slide method. 



the presence of numerous types of actino- 

 mycetes received considerable attention. 



Highly significant in this connection was 

 the contril)ution of Krainsky. His paper pub- 

 lished in 1914 may be considered as a classic 

 on a p.ir with the contril)utions of Cohn, 

 Harz, Thaxter, and Beijerinck. It opened 

 new pathways in th(> development of our 

 knowledge of the actinomycetes. Krainsky 

 emphasized that the voluminous literature of 

 the actinomycetes contains little of a physi- 

 ological nature; the numerous descriptions 

 of different species are so much alike that 

 one gains the impression that there are no 

 proper characteristics for distinguishing dif- 

 ferent kinds of actinomycetes. He empha- 

 sized that the terminology as well had not 

 been sufficiently established. Numerous ac- 

 tinomycetes have been isolated, without rec- 

 ognition of their role in nature, since they were 

 always considered from the point of ^'iew of 

 their pathogenicity and hygienic importance. 



Krainsky's significant contribution was his 

 emphasis of the importance of recognizing 

 the growth characteristics of actinomycetes 

 on synt hetic media. He demonstrated that the 

 nature and concentration of both the carbon 

 and nitrogen sources are of great importance 

 in this connection. The nature of the aerial 

 mycelium, pigmentation of the colony, and 

 the formation of soluble pigment are all con- 

 trolled by the composition of the medium. He 

 further d'^monst rated that the formation of 

 chromogenic pigments on organic media 

 (tyrosinase reaction) is characteristic not of 

 one but of seA'eral species. The formation of 

 invertase and diastase w'as also found to be 

 characteristic of different species. 



Krainsky further established the ability of 

 certain actinomycetes to decompose proteins 

 and cellulose and to reduce nitrate and even 

 suggested the possibility of their being able 

 to utilize the resistant lignin. As a result of 

 these studies he came to the conclusion that 

 the actinomycetes are represented in nature 

 by many distinct species. He suggested that 



