llctcrotropliic l^acteiia 73 



tion docs not necessarily accompany rapid growth. The urea bac- 

 teria differ in their oxygen tension: most of them are aerobic, although 

 the amount of oxygen required may be rather small. 



The urea bacteria have a pH limit of 6.6 for Urobacillus duclauxii, 

 7.0 for Ur. maddoxii, and 8.1 for Ur. pasteurii. The favorable effect 

 of acid peat in prc\enting losses of ammonia from manure is be- 

 lie\'ed to be due to the checking of the growth of the urea bacteria. 



Anaerobic Bacteria. By selective culture methods, Diiggeli 

 found the following numbers of anaerobic bacteria per gram of soil: 

 1,000-1,000.000 but>Tic acid, 0-1,000 cellulose-decomposing, 100- 

 1,000,000 nitrogen-fixing, 100-1,000,000 protein-decomposing, and 

 100-1,000,000 pectin-decomposing forms. By the deep tube method, 

 only between 19,000 and 900,000 anaerobic bacteria were found per 

 gram of soil. No single solid medium can be devised which would 

 be fa\orable for the development of all anaerobic bacteria. 



These bacteria take an active part in the composting of manure 

 in the heap, whenever there is an insufficiency of aeration. The 

 phenomenon of "putrefaction" is chiefly a result of the decomposi- 

 tion of proteins under anaerobic conditions, due to incomplete oxida- 

 tion resulting from insufficient aeration. The absence of air in the 

 deeper layers of the manure pile, the slightly alkaline reaction, and 

 the presence of large amounts of undecomposed organic substances 

 make conditions favorable for the development of anaerobic bacteria. 

 Various anaerobic urea bacteria and thermophflic organisms also 

 find conditions in the composting manure heap favorable for their 

 development. 



Well-rotted horse manure contains spore-forming, anaerobic, 

 thermophilic bacteria, the limiting temperature for their growth be- 

 ing 60-65°C and the thermal death point 110-120°C. Some of these 

 organisms are actively proteolytic. A number of anaerobic spore- 

 bearing bacteria are no doubt brought into the soil in great abun- 

 dance with the feces; certain types have been found in intestinal 

 excreta. 



The role of anaerobic sulfate-reducing bacteria in bringing about 

 iron corrosion appears to be very important. Localized anaerobiosis 

 is believed to exist in the vicinity of buried jDipes; in the presence 

 of sulfate and a certain amount of organic matter, the bacteria are 

 able to bring about the formation of hydrogen sulfide, which will 

 precipitate the iron dissolved from the pipe to give iron sulfide. 



Various anaerobic pathogenic bacteria are able to survive in the 

 soil. Clostridium welchii was demonstrated in 100 per cent of all 



