CHAPTER IX 



GERMS AND DISEASE 



GERMS 



Protozoa are one-celled animals of microscopic size. The 

 one cell performs all the functions necessary for the life of the 

 protozoon. 



They look very often like a tiny mass of clear jelly. In fact, 

 they are the smallest of all animals. Some can be barely seen 

 with the naked eye, others are so small as to look like tiny specks 

 under the most powerful microscope. 



Protozoa live abundantly in water, but they also grow in the 

 bodies of men and animals, causing some of the worst germ dis- 

 eases known. 



Bacteria are minute one-celled plants visible only through the 

 compound microscope. They are found everywhere, in the air, 

 water, and soil, as well as in the bodies of living animals and plants, 

 and in products obtained from them. 



Bacteria cause decay, sometimes a fermentation, and cause many 

 diseases of plants and animals. Other names for bacteria are germs 

 or microbes. Useful bacteria cause decay of dead matter which can 

 then be used by growing plants. In the preparation of vinegar, 

 cheese and butter, bacteria are necessary. Food for certain plants 

 can be produced only by bacteria in the soil. 



Many bacteria are harmless, but there are about twenty, which 

 are capable of producing disease in man. 



There are two classes of bacteria: 



1. Saprophyte, a micro-organism which derives its food from 

 decaying animal or vegetable matter. Examples are: mushrooms, 

 and mold on bread or cheese. 



2. Parasite, an organism which inhabits another organism. For 

 example ; nearly all of the disease -producing bacteria are parasites, 



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