Just as each kind of fermentation possesses a definite organized ferment, so many diseases are dependent on the presence of a distinct microbe; and just as the gardener can pick out and grow a given plant or vegetable, so the bacteriologist can (in most cases) eliminate the adventitious and grow the special organism - in other words, can obtain a pure cultivation which has the power of bringing about the special disease.
This is also caused by the presence of a microbe, of which the virus can also be attenuated, and by inoculation of this weakened virus the animal rendered immune.
It is no less than a cure for the dread disease of hydrophobia in man and of rabies in animals; and the interest of the achievement is not only that he successfully combated one of the most mysterious and most fell diseases to which man is subject, but also that this was accomplished in spite of the fact that the special microbe causing the disease had not been isolated.
The danger from this source is remote, as the microbe does not form spores within the animal body.
In the majority of instances, however, no local indication could be found marking the point at which the microbe was implanted."