74 



Occurrence of Microorganisms in Soil 



soils examined, CI. piitrificus verucausus in 71 per cent, CI. putrificus 

 tenuis in 21 per cent, CI. amylobacter in 65 per cent, CI. tetanomor- 

 plium in 14 per cent, and CI. tetani in 11 per cent of the soils. 



Cellulose-Decomposing Bacteria. Cellulose decomposition in 

 nature is carried out by numerous groups of microorganisms. Among 





..""-'•n 







Fig. 32. 



Anaerobic, cellulose-decomposing bacterium, Bacillus ccUulosac dis- 

 solcens (from Khouvine). 



these, bacteria occupy a prominent place. The anaerobic bacteria 

 were at first believed to be the most important agents in the decom- 

 position of cellulose. It was later found, however, that aerobic 

 bacteria and various fungi are far more important than the anaerobic 

 bacteria. In peat bogs, however, and in the digestive tracts of ani- 

 mals, the anaerobic bacteria are most active. In addition to these, 

 certain special groups of bacteria are often recognized, such as the 

 thermophilic forms, actively concerned with the decomposition of 



