CHANGES BROUGHT ABOUT BY NON-PATHOGENIC ORGANISMS 63 



of particular economic importance, namely lactic, acetic, and 

 butyric. A great variety of others are occasionally produced, 

 usually in small quantities only. 



B 



Fig. 28. Lactic acid bacteria: A, Streptococcus lacticus; B, Bacillus bulgaricus. 



Lactic Acid. Dextrose and some other monosaccharids are 

 converted into lactic acid by several common organisms. The 

 reaction may be empirically represented as follows: 



C 6 H 12 O 6 = 2C 2 H/OH-COOH. 



Dextrose. Lactic acid. 



The reaction occurs most frequently in milk which is allowed to 

 stand. In this case the lactose or milk-sugar is first broken 

 down into the monosaccharids before being converted into lactic 



acid. 



C I2 H 22 U + H 2 = C 6 H 12 8 + C 6 H 12 6 . 



Lactose. Dextrose. Galactose. 



The formation of lactic acid in milk is of the greatest economic 

 importance, as the organisms which produce this acid are the ones 



Fig. 29. Acetic acid organism, Bacillus aceti: a, Normal individuals; b, in- 

 volution forms. (Adapted from Hansen.) 



which are necessary to the development of proper flavors and 

 quality in butter and cheese. This acid is also produced in 

 the manufacture of sauer-kraut and to some extent in silage. 

 The lactic acid formed in milk is instrumental in preventing the 

 growth of putrefactive and other undesirable bacteria. 



