CHAPTER XVI 



DISEASE BACTERIA 



The bacteria hitherto studied are all saprophytes. There 

 remain for consideration those that can carry on their life 

 within the body of living animals and plants, namely, the 

 parasites. The distinction between parasites and sapro- 

 phytes is not a sharp one, for while some species can live 

 only in lifeless material, and others only in living material, 

 there are many that can live either a parasitic or sapro- 

 phytic life. When the bacteria grow in the body of a 

 living animal or plant, they may give rise to disease, and 

 these parasitic bacteria are therefore called disease germs, 

 pathogenic bacteria, disease bacteria, etc. 



How Bacteria produce Disease 



The disease germs are all capable of growing and multi- 

 plying in the body, but the habits of different species of 

 disease bacteria are widely different. Sometimes they be- 

 come distributed all over the body, developing rapidly in 

 any part, perhaps even in the blood. In such cases the 

 disease produced by them is not located at any particular 

 point, but distributed all through the body. This is true 

 of certain forms of so-called blood poisoning, or septiccemia. 

 On the other hand, it sometimes happens that the micro- 

 organisms become located in very definite parts of the 



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