STREPTOMYCES 



365 



there. They concluded that many of the thermophilic actinomycetes 

 found by former workers in composts and self-heating straw and hay 

 were species of Micromonospora. Still more recently Erikson ' has 

 found that Micromonospora species are common in a lake bottom 

 where they apparently take part in the decomposition of cellulose and 

 especially of chitin, during the seasons of the year that the mud is 

 partially aerobic. Obviously this is a genus that will be met with in 



Fig. 133. Micromonospora sp. from lake bottom mud. Waksman's collection. 



the literature in the future as it seems to be common and important, 

 and to include species which are able to grow at high, medium, and 

 low temperatures. 



Streptomyces. Streptomyces has only recently ^° been created as 

 a genus. Most of the non-medical literature is on this section of 

 the inclusive genus Actinomyces, and it is under this latter generic 

 name that most of the past literature will be found. It is very 

 strange that such numerous and ubiquitous organisms remained for 

 so long unknown to so many bacteriologists. It was only after 

 Krainsky, Conn, and Waksman (1914-1918) had shown how numer- 

 ous they were in the soil— they make up 20 to 50 per cent of the 

 colonies that appear on agar plates poured from soil dilutions — that 

 soil bacteriologists realized that they were common soil organisms. 

 They are air (or dust) organisms as well, and any agar plate that is 

 purposely or inadvertently left exposed to the air is likely to show 

 several colonies of Streptomyces. Even so, bacteriologists who are 

 familiar with many less common saprophytic contaminants are fre- 

 quently heard to express the opinion that "actinomycetes are mostly 

 pathogenic and are rare." These soil-inhabiting and air-borne Strep- 



