CHAPTER XI 



BACTERIA, AND WHY CLEANLINESS IS NECESSARY 



OVER three hundred years ago a scientist living in 

 Holland startled the world by announcing that there 

 was life in matter, which we could not see. 



Later on another scientist named Cohn was 

 able to prove its presence by the aid of the micro- 

 scope. But of late years it has been left to Pasteur 

 to demonstrate actually the presence of this life by 

 making living cultures of these organisms in different 

 forms. It is not known whether these organisms 

 belong to animal or plant life, but they are known 

 to be present in different substances in three forms 

 known as Bacteria, Yeasts, and Moulds. In dairy 

 work it is chiefly the bacteria with which we have 

 to deal, and there are many endless varieties of 

 these, but they are divided into two main groups 

 known as ^robic and Anaerobic. The aerobic 

 bacteria are distinguished from the others because 

 they thrive and multiply in the presence of air, 

 while the anaerobic do not thrive where there is 

 air. Both these groups, however, have the means 

 of adapting themselves to the condition in which 



