CHAPTER III. 

 ^Decomposition of 



We saw a short while ago that all decomposition of 

 organic matter is to be attributed to the influence and. 

 activity of bacteria, and when we see that milk, soon 

 after having been drawn, may contain such enormous 

 numbers of bacteria, it is not to be considered strange 

 that it should soon spoil. The first noticeable act of 

 vitality of these inhabitants of milk is generally the 

 souring of the milk, /. c., the transformation of milk 

 sugar into milk acid. A considerable number of such 

 bacteria are now known which cause this transforma- 

 tion, and we know of them further that they have 

 only this effect and no other. In the course of this 

 milk acid fermentation, as we often hear it called, not 

 all of the milk sugar is transformed into milk acid 

 but only a certain part of it ; in other words, a certain 

 amount of milk acid is only formed and after its for- 

 mation the fermentation or transformation comes to a 

 standstill. Bacterial life has ceased to make itself 

 felt, or, to use the expression of the renowned French' 

 scientist, Pasteur, "the acid ferment ( fenucnl lac- 

 tiquc] has become latent." 



The forming of milk acid is, then, the cause of the 

 casein, the most important of the albuminoids of milk, 

 being liberated from its affinity with lime, and the 

 milk "curdles." This kind of curdling is essentially 



