14 Agricultural Bacteriology. 



found in the waters of rivers, especially those of con- 

 siderable size, and in lakes is usually small since there 

 are many factors that tend to destroy the bacteria. 



Most of the other places in which the bacteria are 

 found are not to be looked upon as natural habitats, 

 Tjut rather as secondary sources. The bacteria may ba 

 found almost anywhere, because dust from the soil finds 

 its way into or onto every object. The bacteria of the 

 air come from the soil, being carried up by air currents. 

 The number in the air depends on the amount of dust 

 present; hence, in cities many are found in the air, in 

 the open country far less, and in the air over large bodies 

 of water, none may be present. 



The bacteria found in all articles of food come from 

 one of the natural habitats of this form of life. By 

 keeping foods as clean as possible a great deal can be 

 done to preserve them. 



