HOW BACTERIA MULTIPLY 



209 



vegetables are other instances of the destructive work of 

 bacteria. 



155. How Bacteria Multiply. Bacteria thrive and mul- 

 tiply under proper conditions of food, heat, and mois- 

 ture. With a strong 

 microscope they may be 

 observed to elongate 

 somewhat. A deepening 

 groove, extending cross- 

 wise near the middle, 

 begins to appear in the 

 individual bacterium. 

 In a half hour, if the 

 conditions are favorable, 

 the groove may have 

 deepened to the center, 

 so that the parts will 

 move apart and form 

 two bacteria. At the 

 end of another half hour, 

 each of these may have 

 divided again, and the 

 process may continue in- 

 definitely. The more 

 bacteria, however, the 

 greater the demand for 

 food ; and since the 

 available food supply 

 may be limited, the 

 growth and multiplication of bacteria find natural limits. 



When subjected to unfavorable conditions of food, heat, 

 or moisture, certain kinds of bacteria surround a portion 

 of their bodies with a thick waxy coat, which enables 

 them to withstand the rigors of freezing weather indef- 



COMPOUND MICROSCOPE. 

 Used to detect minute objects. 



