CHAPTER II. 

 PRODUCTS OF METABOLISM. 



THE CHEMICAL EQUATIONS OF FERMENTATIONS. 



The metabolism of all organisms is considered to be a chemical process 

 which follows in all respects the laws of chemistry. That we are not 

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

 are dealing with unknown forces, but simply because we do not know 

 all the factors involved in the process. Some of the chemical changes 

 caused by the living cell can be imitated exactly by the chemist in a test- 

 tube. This may be illustrated by the oxidation of alcohol to acetic acid, 

 the decomposition of urea to ammonium carbonate and of ammonia to 

 nitrate. Some other processes are not as fully understood and not as 

 easily imitated. The alcoholic and acid fermentations of sugars are of 

 such nature. There is no reason to suppose, however, that these processes 

 are other than chemical changes. A chemical process can always be 

 expressed by a chemical equation, consequently the various known 

 fermentations and decompositions caused by microorganisms should be 

 represented by chemical equations. 



This formulation is not always simple, because the greater number 

 of microorganisms decompose organic substances in more than one way. 

 Also, certain compounds may be produced in such small quantities as to 

 escape the chemical analysis entirely, since the determination of many or- 

 ganic compounds is a very difficult task. Again, part of the decomposed 

 material will usually be assimilated in the growth of the cells; hence more 

 material disappears than can be accounted for by the fermentation pro- 

 ducts. There are several possibilities for discrepancies; accurate equa- 

 tions can be given only for the simplest fermentations, the products of 

 which can be analyzed more or less exactly. 



The best studied microbial process is the alcoholic fermentation, 

 which is not only the classical example of fermentation, but also of great 

 commercial importance. The simplest equation for the decomposition 

 of dextrose into alcohol and carbon dioxide by yeast is 



C 6 H 12 O 6 = 2C 2 H 5 OH+ 2CO 2 

 180 92 88 



101 



