298 AGRICULTURAL BACTERIOLOGY. 



from putrefaction, and at the same time to impregnate them 

 with specially desired flavors, by causing them to undergo a 

 fermentation of which the production of lactic acid is a promi- 

 nent feature. We have already noticed how the growth of 

 lactic bacteria in milk prevents the growth of other bacteria, 

 and delays, or wholly prevents, the putrefaction which would 

 occur if the lactic bacteria did not grow and produce an acid. 

 If various forms of vegetables which decay readily arc caused 

 to undergo a proper acid fermentation, they may be preserved 

 a long time. 



III. SAUERKRAUT. 



Pernaps the most common preparation "of this sort is sauer- 

 kraut, a fermented food quite popular with some people. This 

 is made of cabbages which are packed away in proper vessels 

 and mixed with a certain amount of salt. The nature of the 

 fermentation which occurs in the cabbage is very little under- 

 stood. Acids are developed, and the chief agency in the 

 formation of the food has been commonly attributed to lactic 

 bacteria. There has been at present, however, very little care- 

 ful study of this type of fermentation. One species of bac- 

 terium and two species of yeast have been found in the fer- 

 menting sauerkraut and are believed to be its cause. The 

 fermentation appears to be practically identical, whether the 

 material is supplied with oxygen or not, either aerobic or 

 anaerobic fermentation being consistent with the production of 

 the typical fermentation. The bacteria rapidly develop acid 

 up to a certain grade of acidity, but after this grade is reached 

 the bacteria cease to grow and soon die. The final material 

 does not contain bacteria in very great abundance. The yeasts 

 produce some alcohol, and CO 2 and CH 4 are liberated from 

 the fermenting material in quantity. Beyond the few facts 

 here mentioned, little is known in regard to the formation of 

 this material. 



