Waksman 



— 136 — 



Actinomycetes 



were rapidly replaced by an abundant population of actinomycetes. 

 Specific forms could be recognized, by means of this method, and 

 studied in detail. 



The plate method has been used most commonly to study the abun- 

 dance of actinomycetes in the soil and to isolate specific organisms. 

 Synthetic media were found to be highly favorable for the development 

 of these organisms. Some forms grow readily on virtually all common 

 media, whereas others require either certain specific media or special con- 

 ditions of growth. The actinomyces colonies can easily be distinguished 

 from those of bacteria, a somewhat longer period of incubation usually 



Fig. 31. Relation between density of vegetativi 

 actinomycetes Qroni Jensen, 192). 



lyceli 



id plate counts of 



being required. This method also has certain limitations, the most im- 

 portant of which is the lack of differentiation between spores and my- 

 celium. A colony of an actinomyces may originate from a single spore 

 or from several spores or from a piece of mycelium. Not all spores are 

 capable of germinating on a given plate and developing into colonies. 

 The numbers thus obtained represent only a minimum content of actino- 

 mycetes in a given quantity of soil, or only a fraction of the mass of 

 actinomycetes. This method has been used most extensively, however, 

 for the evaluation of the actinomyces population of the soil. 



Ah^indance of actinomycetes.— Hiltner and Stormer (172), in 

 1902, made the first comprehensive survey of the abundance of actino- 

 mycetes, as compared to that of bacteria, in the soil. In the spring of the 



