FERMENTATION OF POLYSACCHARIDES 227 



animals, consequently changes brought about by micro- 

 organisms are of considerable economic importance. 



Fats are glycerides of the fatty acids. Among the com- 

 moner fats are palmitin (C 15 H 31 COO) 3 C 3 H 5 , and olein 

 (C 17 H 33 COO) 3 C 3 H 5 . 



The fermentation of fats is usually primarily an hydroly- 

 sis of the fat into its constituent fatty acids and glycerin. 

 This process may be illustrated by the following reaction: 



(C 17 H 35 COO) 3 C 3 H 5 + 3H 2 - C 3 H 5 (OH) 8 + 3C 17 H 35 COOH 

 Stearin Glycerin Stearin acid 



Microorganisms may then attack either the glycerin or the 

 fatty acid, bringing about secondary fermentation. 



The list of bacteria capable of bringing about fat hydrol- 

 ysis is not very extensive. Many species of molds, however, 

 are known which can bring about this change. It may 

 readily be observed by growing the organism to be studied 

 upon an agar plate, in which the agar contains an emulsion 

 of the particular fat to be studied. The development of the 

 characteristic enzyme, lipase, will give rise to a transparent 

 area immediately surrounding the colony of the lipolytic 

 organism. 



Very few microorganisms are known which can directly 

 digest or ferment fatty acids with long carbon chains. A 

 considerable number of molds and bacteria, however, are 

 able to utilize the volatile acids of the fatty acid series. It 

 has already been noted that molds and bacteria may oxidize 

 acetic acid, butyric acid and their salts. 



Many species of bacteria are capable of fermenting 

 glycerin. This may be regarded as a simple carbohydrate. 

 It is one of the substances frequently used in the laboratory 

 for differentiating the fermentative powers of microorgan- 

 isms and for consequent characterization of species. 



