CHAPTER IV 



PRODUCTS OF MICROBIAL ACTIVITIES* 

 GENERAL CONSIDERATIONS 



The great difference in the metabolism of animals and of bacteria, 

 even though they feed essentially on the same foods, is the incomplete 

 metabolism of most bacteria, contrasting sharply against the very 

 complete oxidation of food in the animal body. The food of the animal 

 is decomposed by the body cells to carbon dioxide, water and urea. It 

 is the most complete decomposition possible, excepting urea which, 

 however, is very near the final decomposition product, ammonium 

 carbonate. Microorganisms, on the contrary, are characterized by 

 incomplete metabolism. They do not commonly oxidize their food to 

 the end products but many of them produce organic compounds which 

 are not farther decomposed by them. It is this partial decomposition 

 of organic matter which makes microorganisms play such an important 

 role in life and industries. Our modern microbiology is dated from the 

 time when Pasteur showed that the alcohol in the beer fermentation, 

 the lactic acid in the souring of milk, the acetic acid in the vinegar 

 fermentation are products of microbial activity. The existence of 

 microorganisms had been known for nearly 200 years, but they were 

 considered largely as a curiosity; as soon as they were recognized as 

 the cause of fermentations, and of toxins, they received at once the 

 greatest attention. Not all bacteria cause incomplete decompositions ; 

 some oxidize as completely as animals do. Others, again, form first 

 intermediary products, which they later decompose completely; among 

 these, are found many molds, the sulphur bacteria, and some species of 

 the vinegar bacteria. 



THE CHEMICAL EQUATIONS OF FERMENTATIONS 



The metabolism of all organisms is considered to be a chemical 

 process which follows in most respects the laws of chemistry. That 

 we are not familiar with all the changes taking place in the cell is not 



* Prepared by Otto Rahn. 



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