296 MICROBES, PEBMENTS, AND MOUI.DS. 



it is indispensable to submit it to the test of the four 

 following rules, which have been clearly established 

 by Koch : — 



1. The microbe in question must have been found 

 either in the blood or tissues of the man or animal 

 which has died of the disease. 



2. The microbe taken from this medium (the 

 blood or tissues, whichever it may be), and artificially 

 cultivated out of the animal's body, must be trans- 

 ferred from culture to culture for several successive 

 generations, taking the precautions necessary to 

 prevent the introduction of any other microbe into 

 these cultures, so as to obtain the specific microbe, 

 pure from every kind of matter proceeding from the 

 body of the animal whence it originally came. 



3. The microbe, thus purified by successive cultures, 

 and reintroduced into the body of a healthy animal 

 capable of taking the disease, ought to reproduce the 

 disease in question in that animal with its charac- 

 teristic symptoms and lesions. 



4. Finally, it must be ascertained that the microbe 

 in question has multiplied in the system of the animal 

 thus inoculated, and that it exists in greater number 

 than in the inoculating liquid. 



These four conditions are necessary and sufficient, 

 and in the present state of science they may be 

 regarded as fulfilled in a considerable number of 

 diseases: in anthrax, fowl cholera, swine fever, 

 glanders, small-pox, tuberculosis, erysipelas, and even 



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