MICROBES AND CONTAGIOUS DISEASES. 
417 
it must be submitted to the test of the four following rules, so 
positively established by Koch : 
1. The microbe must have been found in the blood, in the 
tissues of the diseased individual, or of one dead by the disease. 
2. Obtained from these media, (blood or tissues, as the cam 
may be) and cultivated artificially, outside of the animal, the mi¬ 
crobe ought to be carried from culture to culture for several suc¬ 
cessive generations, taking all necessary precautions to prevent 
the introduction of any other microbe in the same cultures and 
conducting the process in such a manner as to obtain the specific 
microbe wholly free from contamination or mixture with any 
other substance contained in the body which has furnished the 
original. 
3. Thus purified by successive cultures, the microbe, when in¬ 
troduced into the body of a sound animal, which yet is subject to 
the disease, is capable of reproducing in this animal the original 
disease witli all its symptoms and characteristic lesions. 
4. It is also necessary to determine that the microbes developed 
in the animal thus inoculated must be in excess, as to number, 
of those which were introduced by the original inoculation. 
These four conditions are necessary, and they are sufficient, and 
when the necessary experiments have been conducted with a due 
respect to their details, and with uniform exactness, the result 
has been identical, and has consistently and clearly established 
the fact that a true classification of diseases has fixed the place 
of anthrax, chicken and hog cholera, glanders, variola, tubercu¬ 
losis, erysiphla and even Asiatic cholera, as certainly microbic 
diseases in the true acceptation of the word. 
The opposition encountered bv the microbic theory among 
pathologists has nothing new in it, and should not excite any 
one’s surprise. The profession have tenaciously clung to their 
old habits and traditions, and have not surrendered them with¬ 
out much struggling. The parasitic theory is, no doubt, too 
simple and too natural to be accepted without contention. 
But the conquests already made are full of good promise for 
the future. Is it necessary to enumerate them again ? In the 
beginning of this century—for example—the parasitic theory of 
