SECTION III 



BACTERIA AND THE RESISTANCE OF THE ANIMAL 

 BODY TO DISEASE 



CHAPTER XII 



BACTERIA AND DISEASE; GENERAL CONSIDERATIONS 



Koch's Rules. The proof of the germ theory of disease may be 

 dated from 1876, when Koch succeeded in demonstrating the rela- 

 tionship of Bacillus anthracis to the disease anthrax. He later 

 formulated the rules (which are known as Koch's rules) for the 

 determination of the specific relationships of an organism to a 

 disease. They may be stated as follows: 



1. The suspected organism must be found in every case of the 

 disease under consideration. 



2. The organism must be isolated and grown in pure culture. 



3. Inoculation of the organism into suitable animals should 

 reproduce the disease. 



4. The organism must again be isolated from such animals. 

 Unfortunately, the proof of the cause is still lacking in a good 

 many diseases, and is unsatisfactory in others. There are several 

 reasons for this: 



(a) The organisms in some cases have been shown to be ultra- 

 microscopic and capable of passing through a porcelain filter, as, 

 for example, those which cause rinderpest and hog-cholera. 



(6) Some organisms, although evidently not ultramicroscopic, 

 have never been satisfactorily demonstrated under the microscope, 

 possibly from lack of proper staining methods. 



(c) Some organisms are specific for man and do not repro- 

 duce disease of the same type when inoculated into animals. 

 With some of these, accidental or intentional inoculation into 

 man has supplied the needed evidence. 



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