PRODUCTS OF METABOLISM l6l 



Third stage: CeHuOo = 2H2 + 2CO2 + CHsCHaCHaCOOH. 



Kruse has called attention to the fact that these complex equations 

 can well be explained as the simultaneous occurrence of the following 

 simple fermentations: 



CsHiaOs = 2H2 + 2CO2 + CH3CH2CH2CO2H 



C6H12O6 = 3CH3CO2H 



CeHiaOe + 6H2O = 6CO2 + 12H2 



The first fermentation continues when the others have already ceased, 

 and thus the last stage of Perdrix's equations is very simple. Brede- 

 mann also found that the proportion of the various products formed by 

 B. amylobacter varies greatly with the conditions, and the same has been 

 recently established in the fermentation of B. coli. 



Other complications occur when an organism is able to use its own 

 products as food, as is the case with some acetic bacteria. They will 

 at first produce considerable amounts of acetic acid and after a while 

 they oxidize the acid completely. It becomes impossible to account for 

 microbial activity by a chemical equation when several organic com- 

 pounds are decomposed at the same time as is found to occur in some 

 foods, as butter, cheese, ensilage and in sewage. It is also impossible 

 to formulate exactly decompositions which are caused by mixed cultures. 

 The complications become so great and the relations between different 

 orgatiisms are so little known that it is useless to make the attempt. 



Physiological Variations 



The great variabiUty of microorganisms in morphological respects 

 has abready been pointed out in Part I of this book. A similar variation 

 and adaptation are noticed in their physiology, especially with the food 

 substances of bacteria and consequently with their metabolic products. 

 Microorganisms change their physiological properties very readily with 

 the environment; the new variety may keep its acquired properties for 

 some time even if brought back to the original conditions. It is stated 

 frequently that microorganisms tend more toward variations than the 

 more complex organisms. It should be considered, however, that the 

 experiences in the variations of green plants and animals are based on 

 individuals, while in the case of microorganisms these experiences are 

 gained almost always from millions of cells. A simple illustration is the 

 11 



