10 Historical 



"putrefactions" due to living organisms was soon followed by that 

 of Kiitzing, in 1837, on the production of acetic acid. In 1841, 

 Boutron and Fremy studied the formation of lactic acid from sugar; 

 in 1844, Pelouze and Gelis studied the formation of butyric acid 

 under anaerobic conditions; and, in 1850, Mitscherlich made a care- 

 ful investigation of the decomposition of the cell wall of plants by 

 microorganisms. 



Although Mitscherlich emphasized in 1843 that the two well- 

 known decomposition processes, designated as "fermentation" and 

 "putrefaction," were brought about by two different groups of micro- 

 organisms, the first by yeasts and the second by vibrios, it remained 

 for Pasteur to elucidate clearly in 1857 the principle of anaerobiosis 

 or life without atmospheric oxygen. These two men thus clearly 

 indicated the role of microorganisms, especially of bacteria, in a 

 number of processes which are found to be of the greatest importance 

 in the soil. Mitscherlich emphasized the role of bacteria in the de- 

 composition of carbohydrates, and Pasteur the role of bacteria and 

 other microorganisms in the decomposition of urea and other ni- 

 trogenous materials, processes of great importance in the degradation 

 of plant and animal residues in soils and in composts. 



Foundation of Soil Microbiology (1861-1890) 



About the middle of the last century three distinct biological 

 processes had been clearly outlined and were partly understood. 

 These were decomposition of organic matter, nitrification, and nitro- 

 gen fixation. 



Organic matter decomposition was known to give rise to humus, 

 which was believed to be one of the fundamental factors in soil 

 fertility. Some investigators considered that humus was only an 

 intermediary product and not a plant food. Organic matter was 

 believed by chemists to decompose slowly by chemical oxidation. 

 The work of Wollny and others finally led to a better understanding 

 of the microbiological nature of the process. 



The accumulation of nitrates in the soil as a result of decomposi- 

 tion of organic matter was known in the seventeenth and eighteenth 

 centuries, but only Boussingault and Schloesing connected this process 

 with soil fertility. Thus began a series of studies on nitrification 

 which was to have an important eft'ect upon our knowledge of soil 

 microbiological processes. 



