CHAPTER XXI 

 PATHOGENIC BACTERIA 



Introduction. Definitions. Those bacteria which pro- 

 duce morbid changes in the animal or plant body, under 

 natural conditions or under conditions artificially produced 

 by inoculation, are called pathogenic bacteria. The term is 

 relative and applicable only within certain limits. Some of 

 the ordinarily harmless bacteria, when introduced into the 

 body of the animal or plant in large numbers, produce mor- 

 bid affects. There is, also, no one pathogenic bacterium 

 which will produce diseased conditions in all animals or plants. 

 Some varieties of bacteria are pathogenic for one species of 

 animal or plant and non-pathogenic for others. 



The term pathogenic has come to be usually applied to a 

 bacterium, or other microogranism, which produces disease 

 under normal conditions. 



Many saprophytic bacteria are pathogenic for man and for 

 some species of animals and plants. These bacteria may ac- 

 cidentally gain entrance into the tissues of the body or may 

 be introduced for experimental purposes. Bacteria of this 

 class are called facultative parasites. There are still other 

 bacteria which give all the evidences of being parasites, nor- 

 mally, but often, for varying periods of time, may live as 



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