CHAPTER VIII 



THE RELATION OF BACTERIA TO DISEASE. INFLAM- 

 MATION 



WE have already called attention to the fact that 

 only a small proportion of the known bacteria are 

 producers of disease, i. e., are pathogenic. In order 

 to prove positively that a disease is due to a certain 

 bacterium it is absolutely necessary that this bacterium 

 be always found in the disease. Furthermore, it must 

 be possible to reproduce the same disease by the injec- 

 tion of pure cultures of the bacterium, and from the 

 diseased tissues thus produced it must be possible to 

 again isolate the germ. 



The manner in which the various bacteria produce 

 disease, their entrance into the body, the part of the 

 body commonly attacked, all these differ considerably 

 with the different micro-organisms. Some, like the 

 bacillus of diphtheria and the bacillus of tetanus (lock- 

 jaw), secrete very powerful poisons, and, while these 

 bacteria do not themselves penetrate deep into the body 

 tissues, their poison is absorbed and gives rise to severe 

 symptoms. In the case of other bacteria, for example, 

 the tubercle bacillus, the germs penetrate deep into the 

 body tissues and there multiply. In their growth they 

 give off poisons which cause the gradual destruction of 

 the tissues in which they lodge. In this way the tubercle 

 bacillus causes large parts of the lung to be destroyed or 

 bones to be eaten away, etc. 



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