176 PRINCIPLES OF SOIL MICROBIOLOGY 



incomplete oxidation as a result of insufficient aeration. The absence 

 of air in the deeper piles of manure, the slightly alkaline reaction and the 

 presence of large amounts of undecomposed substances make conditions 

 favorable for the development of anaerobic bacteria. 71 Various anaero- 

 bic urea bacteria 7 ^ and thermophilic organisms 73 also find conditions in 

 the composting manure heap favorable for their development. Well 

 rotted horse manure contains spore-forming, anaerobic thermophilic bac- 

 teria; 74 the limiting temperature for their growth was found to be 60° to 

 65°C. and the thermal death point 110° to 120°C. Some of these or- 

 ganisms were found to be actively proteolytic. No growth took place 

 at room temperature. Various anaerobic spore-bearing bacteria are 

 no doubt brought into the soil with the feces in great abundance; a 

 number of these organisms have actually been demonstrated in intes- 

 tinal secreta. 75 



Physiological activities of anaerobic bacteria. It is impossible to dis- 

 cuss the physiological activities of the various obligate anaerobic bac- 

 teria, since they differ greatly in the nature of their metabolism. Those 

 that obtain their energy from cellulose, those that can obtain their 

 nitrogen from the elementary form, those that can utilize nitrate or 

 sulfate oxygen, and those that produce foul odors from complex proteins 

 have a distinct physiology from one another and cannot be considered 

 under one heading, merely because they are similar in their requirements 

 of oxygen tension. They usually have an optimum range of hydrogen- 

 ion concentration at pH 6.0 to 8.2 with a limiting range of pH 5.0 to 

 9.0; the spores germinate better at a higher acidity, with an optimum at 

 pH 6.0 to 7.2. 76 



While aerobic bacteria produce largely carbon dioxide among the 

 volatile gases, the anaerobic bacteria are characterized by the production 



71 Severin, S. A. Die im Miste vorkommende Bakterien und deren physiolo- 

 gische Rolle bei der Zersetzung derselben. Centrbl. Bakt. II, 1: 799-817. 1895; 

 3: 628-633, 708. 1897. Zhur. Opit. Agron. (Russian), 1: 463-489. 1920. 



"Geilinger, 1917 (p. 210). 



73 Veillon, R. Sur quelques microbes thermophiles strictement anadrobies. 

 Ann. Inst. Past. 36: 422-438. 1922. 



74 Damon, S. R., and Feiber, W. A. Anaerobic sporulating thermophiles. 

 Jour. Bact. 10: 37-46. 1925. 



75 Kahn, M. C. Anaerobic spore-bearing bacteria of the human intestine in 

 health and in certain diseases. Jour. Inf. Dis. 35: 423-478. 1924. 



76 Dozier, C. C. Optimum and limiting hydrogen-ion concentrations for 

 B. botulinus and quantitative estimation of its growth. Jour. Inf. Dis. 35: 105- 

 133. 1924. 



