l66 BACTERIA, YEASTS, AND MOLDS 



the microorganisms will be destroyed, the trouble may 

 be checked and the pickles preserved. It is practically 

 important to know that pickles should not be kept in 

 glazed ware, since the acetic acid may unite with the 

 glazing and make unwholesome products. Glassware 

 receptacles are best for the holding of pickles. 



In a somewhat modified way acetic acid or lactic acid 

 is the basis of certain other preserved foods. Sauer- 

 kraut, for example, is cabbage protected from putre- 

 factive fermentation by allowing it to sour and develop 

 acids. Among these, acetic acid is somewhat prominent, 

 but lactic acid is also found. The acid in this case is 

 formed in the cabbage by the growth of acid-producing 

 bacteria, and after it is formed it prevents the growth 

 of other putrefactive bacteria, thus making it possible 

 to preserve for a long time the vegetable material which 

 would otherwise undergo putrefaction. Here we actually 

 have an instance of one kind of harmless microorgan- 

 ism protecting food from the action of other species. A 

 similar food product is sometimes made from beans which 

 are allowed to sour and are thus preserved from further 

 decay. 



Any substance can be preserved from bacterial action 

 if it can be soaked in vinegar or other acid, and it is 

 therefore possible in the household to co'nvert into either 

 sour or sweet pickles a considerable variety of vegetables. 

 The use of vinegar for this purpose is very limited, 

 mostly confined to green fruits and vegetables, although 

 fish or flesh is occasionally treated in the same way. The 

 product obtained is used as a flavor to our diet rather than 

 as a food. 



