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 

 lie 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 5.5 C. 

 (41.9 F.) and 43 C. (109.4 F.), although species 

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

 others as low as C. (32 F.). 



The bacteria commonly found in soil and water 



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