248 MICROBIOLOGY OF SOIL. 



that about one half of the fermentation products is gaseous and that 

 the other half consists of acetic 'and butyric acids. 



THE OXIDATION or METHANE, HYDROGEN AND CARBON MON- 

 OXIDE. Aside from cellulose, methane may also be produced from 

 various other carbohydrates, organic acids and proteins. Large amounts 

 of methane are thus contributed to the atmosphere by swamps, manure 

 heaps and low-lying meadows. In a purely chemical way methane may 

 also be set free from volcanoes and mineral springs. The constant 

 additions of methane, ethane, hydrogen and carbon monoxide represent 

 a considerable amount of potential energy. It is important to know, 

 therefore, whether these materials are at all utilized. 



That methane may be utilized by bacteria as a source of energy was 

 first shown by Sohngen in 1905. He isolated an organism named by 

 him B. methanicus that showed itself capable of growing in inorganic 

 solutions confined over an atmosphere of methane, oxygen and nitrogen. 

 The methane gradually disappeared and there were formed consider- 

 able quantities of organic matter. The ability to oxidize methane 

 has been claimed for a number of other organisms by Sohngen and 

 others. 



Early observations on the ability of moist soil to cause the oxidation 

 of hydrogen are credited to de Saussure (1838). Many years later (1892) 

 Immendorff called attention to the same fact. It was not, however, until 

 1905 that the oxidation of hydrogen was shown to be a specific biological 

 process. In that year papers by Sohngen and Kaserer reported experi- 

 ments wherein inorganic solutions confined under an atmosphere of hydro- 

 gen, oxygen and carbon dioxide and inoculated with very small quantities 

 of soil developed a bacterial membrane at the surface. The hydrogen 

 was oxidized and organic matter produced at the expense of the energy 

 set free. The observations just noted have been confirmed by other 

 investigators, by means of mixtures and single species of soil bacteria. 

 Finally it should be added here that B. oligocarbophilus previously isolated 

 by Beyerinck and van Delden is able, according to Kaserer, to oxidize 

 also carbon monoxide. 



THE CLEAVAGE AND FERMENTATION or SUGARS, STARCHES AND 

 GUMS. Sugars are a very acceptable source of food and energy for soil 

 bacteria. A culture solution containing suitable mineral salts and sugar 

 ferments readily when inoculated with a small amount of fresh soil. 

 When no combined nitrogen is added, Azotobacter, or B. (Clostridium) 



