MICRO-ORGANISMS AND ENZYMS 29I 



as previously stated, under the general name of fer- 

 mentation. 



(7) Distribution. — Bacteria are found distributed 

 nearly everywhere in the soil, in the air and in water. 

 They are always present in large numbers wherever 

 vegetable or animal matter is undergoing decay. They 

 are, therefore, always closely associated with dirt and 

 filth. While some are the causes of dreaded diseases 

 and of serious troubles in cheese-making, most of 

 them are either harmless or actively helpful in many 

 ways. 



Unorganized ferments or enzyms. — Many enzyms 

 are produced directly by bacteria and are the direct 

 agents producing the observed changes of bacterial 

 activity, while many are formed in higher plants and 

 in animals. Thus, the pepsin found in the human 

 stomach is an enzym; its special power or form of 

 activity enables it to change protein compounds from 

 insoluble to soluble forms. The ptyalin contained in 

 saliva is another enzym and is capable of changing 

 starch into sugar. Enzyms are destroyed by high 

 temperatures and by many disinfectants. Some sub- 

 stances, like ether, chloroform and formaldehyd, do 

 not seriously interfere with the activity of enzyms, 

 while they do destroy bacteria. 



In connection with the subject of ferments, we 

 shall consider the following ones as those of most 

 importance in connection with cheese-making: (i) 

 Lactic acid bacteria, (2) gas-producing bacteria, (3) 

 digesting bacteria, (4) bacteria producing undesir- 

 able flavors, (5) yeasts, (6) milk-enzyms, (7) rennet- 

 enzyms, and (8) pepsin. The ferments that are 



