BACTERIA USEFUL TO MAN 



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Bacteria in Milk. Among the most common bacteria in milk are 

 those which produce lactic acid and cause the milk to sour. Lactic 

 acid bacteria are useful in the stomach, as they oppose other bac- 

 teria which may be harmful or produce putrefaction. 



To-day there are certain types of tablets sold on the market which 

 are supposed to contain bacteria to be taken either in the form of 



FIG. 193. On the left, clover growing in soil uninoculated. On the right, clover 

 growing in soil which has been inoculated. 



a pill or dissolved in milk. The bacteria oppose harmful bacteria 

 found in the body. 



Bacteria in Butter and Cheese. Cheese is usually ripened with 

 the use of molds and bacteria. Some types of cheese, such as lim- 

 burger, are placed in moist cellars from four to six weeks to allow the 

 bacteria to grow. This process is closely related to putrefaction, 

 causing the cheese to have a disagreeable odor. 



