MICROORGANISMS AND FERMENTATIONS U 



FERMENTATION PROCESSES 



The assimilated nutrient substances are employed, partly in 

 building up the cells during growth and reproduction, and partly 

 as sources of energy for these and other vital processes. All 

 substances are not equally suited for both purposes, and distinction 

 may be made between the nutrient substances proper and those 

 which merely function as sources of energy. As long as active 

 reproduction is taking place, a considerable proportion of the 

 latter will be pressed into service as cell-building material, later 

 on to be decomposed into simpler products, when the energy thus 

 liberated will be utilised by the microorganisms. That portion of 

 the period occupied by the reproductive process during which no 

 appreciable amounts of decomposition products are separated is 

 known as the incubation period. The decomposition products, which 

 bear a certain general comparison with the substances contained in 

 the urine of animals, are known as fermentation products, and fer- 

 mentations are to be regarded as decompositions brought about 

 by microorganisms. Exceptions occur when the organic sub- 

 stances undergo complete oxidation to carbon dioxide and water ; 

 such changes are looked on as respiration processes analogous to 

 those observed among the higher organisms. Fermentation thus 

 implies only a partial decomposition through the agency of micro- 

 organisms. It is evident that such a process entails a certain loss 

 of efficiency, and consequently a larger consumption of material. 

 Complete decomposition is only effected by aerobic microorganisms, 

 more particularly by the moulds which, as previously mentioned, 

 are able to form aerial shoots. Moulds only function as fermenta- 

 tion organisms when excluded from access to air, under which cir- 

 cumstances many of them produce alcohol, like the yeasts. It 

 will now be understood that the most typical of the fermentation 

 organisms must be facultative or obligate anaerobes. Fermenta- 

 tions are also known which are simple oxidations, such as the 

 acetic acid fermentation. Processes of this nature require a 

 plentiful supply of air, and can, therefore, only be carried out by 

 aerobic organisms. 



Fermentations and fermentation organisms are often named 

 after their most characteristic products, e.g., alcohol and butyric 

 acid fermentations, lactic acid or butyric acid bacteria. Some- 

 times the name is derived from the substance attacked, e.g., 

 cellulose fermentation or cellulose bacteria. The former system 

 is the more logical. Soil formation is the natural bacterial 

 decomposition of plant remains into products, which, as a 

 rule, are not stinking. Putrefaction is the decomposition of 

 animal remains into products which are usually stinking. As 



