206 BIOLOGY OF SPECIALIZED GROUPS 



of bacteria and some other microorganisms on carbohydrate 

 compounds. 



Various substances are produced during the process of 

 fermentation. Gases may or may not be produced; acids 

 and alcohols and ethers and esters are formed in small quan- 

 tities. The gases which may be produced during fermentive 

 processes are carbon dioxide, oxygen, hydrogen, nitrogen, 

 and methane or marsh gas. Among the alcohols are methyl, 

 ethyl, butyl, propyl, glycerine, and many higher alcohols. 



It should be noted that all fermentation is not due to the 

 enzymes which bacteria produce. A large variety of yeasts 

 and some species of molds are concerned in some fermentive 

 processes. The majority of all alcoholic fermentations are 

 due to yeasts (Saccharomycetes). Some bacteria, such as 

 Bacillus coli, produce small amounts of alcohol. 



The fermentations due directly to bacteria will be briefly 

 considered. The fermentive processes are designated by 

 the most important by-product produced. Thus we speak of 

 lactic acid fermentation, acetic acid fermentation, and butyric 

 acid fermentation. 



It seems that in the majority of bacterial fermentations 

 there is a specific bacterium or group of bacteria which is 

 prominent in the process. 



Lactic Acid Fermentation. The bacteria concerned in 

 this fermentation are very widely distributed. They are 

 found chiefly in milk, but may also occur in other solutions, 

 as, for example, distillery mash. 



