PATHOGENIC BACTERIA 245 



In the case of the infection of the body and the multiplica- 

 tion within the body of Bact. anthracis, the pathogenic 

 effects are probably principally mechanical and due in the 

 main to the rapid multiplication of the bacteria. In this case 

 there is also some form of toxin produced by the bacterial cells. 



The products of the metabolism of the pathogenic bacteria 

 will receive consideration later. 



Proof of Etiological Relationship. In order to prove that 

 a definite microorganism is the etiological factor of a specific 

 disease, Robert Koch devised the following postulates or 

 rules which if fulfilled establishes the connection between a 

 microorganism and a disease. 



(a) The microorganism must be found in the tissues or 

 body of the animal or plant with the disease. 



(6) The microorganism must be isolated in pure culture 

 from the body of the diseased animal or plant. 



(c) It must be grown successfully on culture media. 



(d) It must be able to produce the disease in a healthy 

 animal or plant in approximately the same form and giving 

 the same symptomatology as in (a). It must also again be 

 found in the tissues of the experimental animal or plant. 



The majority of pathogenic bacteria fulfill these laws, but 

 there are some microorganisms which undoubtedly produce 

 specific infectious diseases which do not fulfill the postulates 

 of Koch. The following table gives a partial list of the micro- 

 organisms which produce specific infectious diseases but which 

 are unable to fulfill Koch's laws : 



