Page:Popular Science Monthly Volume 20.djvu/259

Rh decomposition, even in the presence of atmospheric air, any such action being originated and maintained only by the developmental action of definite organic germs.

2. That different kinds of fermentation (using that term in its large sense) are produced by organic germs of different species. Thus, while torula sets going the alcoholic fermentation in a saccharine wort, other fungoid germs will set up the acetous, and others, again, the putrefactive fermentation, when introduced into fluids of the same kind.

3. That many different kinds of germs—notably those of the bacteria, which induce putrefactive fermentation—are constantly floating in the ordinary atmosphere, so as to be almost certainly self-sown in any organic fluid freely exposed to it.

4. That, if these germs be removed by mechanical filtration, or be got rid of by subsidence, or be deprived of their potency by chemical agents which destroy their vitality, the most readily decomposable organic fluid may be subjected to the freest contact with the air from which the germs have been thus eliminated without undergoing any change.

5. That, as there is no such thing as fermentation without the presence of germ-particles, so there is no such thing as the spontaneous origination of such germs, each kind, when sown in the liquid, reproducing itself with the same regularity as in higher plants, and thus continuously maintaining its own type.

6. That such germ-particles, when dried up, can not only maintain their germinal power for unlimited periods, starting into renewed activity so soon as the requisite conditions are supplied, but that, in this state of dormant vitality, they can be subjected to influences which would destroy the life of the growing plants—such as very high or very low temperatures, the action of strong acid or alkaline solutions, and the like.

The first application of these doctrines to the study of disease in the living animal was made in a very important investigation, committed to Pasteur by his old master in chemistry (the eminent and eloquent Dumas), into the nature of the pébrine, which was threatening to extinguish the whole silk-culture of France and Italy. It had been previously ascertained that the bodies of the animals affected with this disease (whether in the worm, chrysalis, or moth stage) swarm with peculiar minute corpuscles, which even pass into the undeveloped eggs of the female moth, but there was no evidence that these corpuscles were independent, self-developing organisms introduced from without, many regarding their presence as a mere expression or concomitant of the disorder, not as its cause. It would be too long to detail the steps of this most complicated and difficult inquiry, and I must satisfy myself with the mere statement that it not only