CHAPTER II 



FACTORS INFLUENCING BACTERIAL GROWTH. 

 DISINFECTANTS. RESULTS OF BACTERIAL GROWTH 



Habitat. Bacteria of one species or another exist almost every- 

 where. Forty different forms have been described as common 

 in soil. They are present in the air in large numbers in populated 

 areas, especially near the surface of the ground. Particles of dust 

 may be laden with them ; anything that tends to set the dust 

 in motion considerably increases the number of bacteria in the 

 air, hence the necessity of sprinkling floors before sweeping and 

 " moist " dusting whenever possible. They are present in the 

 mouth, stomach, and intestines of animals and human beings; 

 on the surface of the skin, under the finger nails, and on the hairs. 

 They are present in rivers, and in the ocean. They are especially 

 abundant in all forms of decaying matter. Everywhere, then, 

 in nature there exists this tremendous force with its wonderful 

 power of multiplication, a power which nevertheless is held in 

 control. 



FACTORS INFLUENCING BACTERIAL GROWTH 



Food. Perhaps the universality of bacteria is explained by 

 the fact that they can utilize the most diverse substances as food, 

 substances varying from the simplest to the most complex nitrog- 

 enous compounds. The presence of nitrogen, however, in some 

 form is indispensable. 



A simple classification of bacteria may be made on the basis 

 of their food requirements. Those which supply their nutritional 

 needs while engaged in disintegrating the lifeless remains of plants 

 or animals are known as strict saprophytes. On the other hand, 



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