CHAPTER IV 



THE EFFECT OF PHYSICAL AND CHEMICAL AGENTS 

 UPON BACTERIA, AND THE EFFECTS OF BACTE- 

 RIAL GROWTH 



Like the higher forms of vegetation, bacteria are 

 susceptible to many influences, the physical and 

 chemical conditions which surround them deter- 

 mining whether they shall live and multiply, or 

 he dormant, or perish. 



Temperature. — Three points of temperature are 

 considered in the growth of different bacteria: a 

 minimum being the lowest point at which growth 

 occurs, an optimum being the temperature of most 

 luxuriant growth, and the maximum being the high- 

 est degree at which growth can take place. 



The extremes of temperature between which the 

 majority of bacteria are known to grow are ^^511^ 

 (41.9° F.) andJ3^_C:_ (109.4° F.), although species 

 exist which may multiply at 70° C. (158° F.) and 

 others as low as 0° C. (32° F.). 



The bacteria commonly found in soil and water 



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