296 MICROBES,.FERMENTS, AND MOULDS. 
it is indispensable to submit it to the test of the four 
following rules, which have heen 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 
