CHAPTER II. 



"JTbe ©rigin of bacteria in fliMlfe ano tbe Conof* 



tions jfavorable for tbetr Breeoing 



ano Multiplying. 



It is a well known fact that milk undergoes a radi- 

 cal chemical change only a few hours after it has been 

 drawn. This change, to onr visible conception, con- 

 sists in the milk becoming sour, in other words the 

 milk sugar has changed to milk acid and, in conse- 

 quence of this acidity, the casein has been separated 

 from its connection with lime and is 'set free — the 

 milk " curdles." We generally notice only this first 

 phase, because in itself it is sufficient to unfit milk 

 for further use. A second phase follows in which the 

 casein is partly dissolved and fermentation sets in, 

 bubbles of gas forming, and the process is wound up 

 with real putrid decomposition and the forming of 

 mould. 



In the microscope we possess an instrument that 

 enables us to enter into a study of the composition 

 and life of the lowest organisms, and also a means to 

 enable us to make and stud)- their culture, through 

 which it has been demonstrated that every process of 

 decomposition of organic matter is due to the action 

 of such organisms and that they, somehow, disin- 



