CHAPTER IV. 



FERMENTATIONS IN MILK AND THEIR 

 TREATMENT. 



IT has been shown in the preceding chapter that the 

 contamination of milk with bacteria occurs so constantly 

 that under normal conditions it always contains a varying 

 amount of germ life. The result of this infection is to 

 cause in the milk, in due course of time, subsequent changes 

 of a fermentative nature. As a rule milk sours, due to the 

 production of acid from the decomposition of the milk 

 sugar; but, not infrequently, this more common change is 

 supplanted by other types of fermentative activity that re- 

 sult in the production of other kinds of by-products. These 

 fermentations are sometimes designated as abnormal, be- 

 cause of their less frequent occurrence. 



It is impossible in the present state of knowledge to sat- 

 isfactorily classify these changes; but provisionally, they 

 may be grouped according to the substances on which they 

 act, or on the basis of the most prominent by-product 

 formed. 



Milk is such a complex substance that the changes pro- 

 duced by a single germ are often so numerous that the 

 processes cannot be separated in their reactions. It must 

 be remembered then, in referring to the different types of 

 fermentations, that perhaps a distinct by-product is being 

 formed, but it is more than probable that there are a series 

 of changes, in which the most marked decomposition by- 

 product is alone taken into consideration. For example, 

 there is a fermentation classed under the head of the bu- 



