DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 317 



fermentation products falls within the limit of error. These experi- 

 ments show that about one-half of the fermentation products is 

 gaseous and that the other half consists of acetic and butyric acids. 



The Oxidation of Methane, Hydrogen and Carbon Monoxide. — ^Aside 

 from cellulose, methane may also be produced from various other carbo- 

 hydrates, 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 consid- 

 erable 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 considerable 

 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 experiments wherein inorganic solutions confined under an 

 atmosphere of hydrogen, 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. 

 oligocarbopMlus previously isolated by Beijerinck and Van Delden is 

 able, according to Kaserer, to oxidize also carbon monoxide. 



The Cleavage and Fekmentation of Sugars, Starches ^and 

 Gums. — Sugars (page 163) 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. 



