BACTERIA AND MILK FERMENTATIONS 43 



which an exceedingly varied and active life is possible. 

 In nature and in many of the arts and industries, 

 bacteria are of the greatest utility, if not indispensable. 

 They play a most important part in the disintegration of 

 vegetable and animal matter, resolving compounds into 

 their elemental constituents in which form they can again 

 be built up and used as plant food. In the art of butter 

 and cheese making bacteria are indispensable. The to- 

 bacco, tanning, and a host of other industries cannot 

 flourish without them. 



II. MII.K FERMENTATIONS. 



Definition. In defining fermentation processes, Conn 

 says that, "In general, they are progressive chemical 

 changes taking place under the influence of certain 

 organic substances which are present in very small 

 quantity in the fermenting mass." 



With few exceptions, milk fermentations are the result 

 of the growth and multiplication of various classes of 

 bacteria. The souring of milk illustrates a typical fer- 

 mentation, which is caused by the action of lactic acid 

 bacteria upon the milk sugar breaking it up into lactic 

 acid. Here the chemical change is conversion of sugar 

 into lactic acid. 



The most common fermentations of milk are the fol- 

 lowing: 



r Lactic. 



I Normal -j Curdling and Digesting. 



I I Butyric. 



Milk Fermentations 



f BiUer. 



I Slimy or Ropy. 

 Abnormal ... -J Gassy. 

 I Toxic. 

 I Chromo<j:cnic. 



