CHAPTER VI. 

 BACTERIA. 



Their three general groups. Forms and growth. How bacteria 

 may be destroyed. Their relation to the fertility of the soil. 

 How decay produced by bacteria increases fertility in soils. 

 Decay of fruits, meats, and vegetables. Various means of pre- 

 serving food. 



Relation of bacteria to dairy products. Part bacteria'play in making 

 butter and cheese. Bacteria in vinegar-making. 



In the air, on the surface of all objects, in water 

 and in most all liquids, and in the soil everywhere, 

 are millions of very small living things called bac- 

 teria, or germs. They are so small that, to see 

 them, one requires the aid of a compound micro- 

 scope. It takes several thousand bacteria, laid side 

 by side or end to end, to make a line an inch long. 

 Small as they are, they exist in such countless 

 numbers that their influence in the world is very 

 great. 



In a very general way it can be said that there 

 are three kinds of bacteria, those that are useful 

 to man, those that are harmful, and those that are 

 neither harmful nor useful. However, when they 

 shall have been studied more, the last kind may be 

 classed with one of the other two. Bacteria are 

 generally thought of as producing disease. It is 

 true that a number of species do produce disease; 



151 



