PRODUCTS OF METABOLISM. 107 



imported from eastern Asia, in such a high degree that they are used for 

 the production of industrial alcohol since they have also, unlike the 

 yeasts, the quality of converting starch. These molds were first called 

 " Amylomyces" though the more modern classification put them in the 

 genus Rkizopus. Among the Aspergillacece, Aspergillus oryzce is the only 

 species which is materially concerned in the production of alcohol. It is 

 found in the fermentation of Japanese rice-brandy, called "Sake," and 

 has been tried in Europe as a substitute for malt to change starch into 

 fermentable sugars. Since these molds make alcohol mainly in the absence 

 of oxygen, when the cells are spherical (gemmae) and look like budding 

 yeasts, it was believed for some time that yeasts were only a certain stage 

 of development of the mucor molds. Alcohol, along with other com- 

 pounds, is also formed by certain bacteria, though in small quantities and 

 not as the only product; this is true in the butyric fermentation, and in 

 gassy fermentations. 



Alcohols other than ethyl alcohol are produced by several organisms. 

 Methyl alcohol (HCH 2 OH) is found to be produced by B. boocopricus from 

 cow-dung. Butyl alcohol (CH 3 (CH 2 ) 2 -CHOH) is a common product 

 in the butyric fermentation. B. amylozyma makes amyl alcohol [CH 3 - 

 (CH 2 ) 3 CH 2 OH] under certain conditions, and it is probable that the 

 fusel oil, the by-product of alcoholic fermentation in distilleries, is not 

 formed by the yeast, but by some anaerobic organisms developing in the 

 fermenting pulps. The use of pure cultures for the production of fusel 

 oil, especially amyl alcohol, has been suggested. 



Besides alcohol, organic acids are very commonly produced from 

 sugar by many bacteria, yeasts and molds. The acid fermentations have 

 wide practical application, and much attention has been paid to their 

 study. If, however, our knowledge, especially of the quantitative 

 relations between food and products, is limited, this is largely due to 

 the great variability of the organisms and the difficulty of analysis. 



The best known, because the simplest, fermentation, is the pure 

 lactic fermentation which has already been discussed on page 102; it is 

 very nearly represented by the equation 



C 6 H 12 O 6 = 2 CH 3 CH(OH)COOH 



Dextrose Lactic acid 



The bacteria which cause this fermentation are called true lactic 

 bacteria. They are the main acid producers in milk. Other acid 

 producers form gas besides lactic acid or other acids or alcohol. In 



