PRODUCTS OF MICROBIAL ACTIVITIES 231 



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. Since a chemical process can always be expressed by a 

 chemical equation, we should expect the same with the fermentations 

 and decompositions caused by microorganisms. 



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 organic 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 products. There are several possibilities for dis- 

 crepancies; accurate equations can be given only for the simplest fer- 

 mentations, the products of which can be analyzed more or less exactly. 



The best studied microbial process is the alcoholic fermentation. 

 The simplest equation for the decomposition of dextrose into alcohol 

 and carbon dioxide by yeast is 



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



180 92 88 



According to this formula, 100 parts of dextrose should give 51.11 parts 

 of alcohol and 48.89 parts of carbon dioxide. The actual yield comes 

 very close to these numbers, but does not reach them; the largest 

 amounts found were 46-47.5 per cent of carbon dioxide and 47.5-48.67 

 per cent of alcohol. Under the most favorable conditions, the total 

 yield of the products of fermentation was only 95 per cent of the 

 theoretical yield. 



Other products are formed besides the alcohol and carbon dioxide. 

 The amount of glycerin found in fermented liquids varies very much 

 with the conditions of fermentation; it reaches from 1.6 to 13.8 per cent 



