If it is a terrifying thought that life is at the mercy of the multiplication of these minute bodies, it is a consoling hope that Science will not always remain powerless before such enemies, since for example at the very beginning of the study we find that simple exposure to air is sufficient at times to destroy them.

But, if oxygen destroys the vibrios, how can septicemia exist, since atmospheric air is present everywhere?  How can such facts be brought in accord with the germ theory?  How can blood, exposed to air, become septic through the dust the air contains?

All things are hidden, obscure and debatable if the cause of the phenomena be unknown, but everything is clear if this cause be known.  What we have just said is true only of a septic fluid containing adult vibrios, in active development by fission:  conditions are different when the vibrios are transformed into their germs, [Footnote:  By the terms “germ” and “germ corpuscles,” Pasteur undoubtedly means “spores,” but the change is not made, in accordance with note 3, above.—­Translator.] that is into the glistening corpuscles first described and figured in my studies on silk-worm disease, in dealing with worms dead of the disease called “flacherie.”  Only the adult vibrios disappear, burn up, and lose their virulence in contact with air:  the germ corpuscles, under these conditions, remain always ready for new cultures, and for new inoculations.

All this however does not do away with the difficulty of understanding how septic germs can exist on the surface of objects, floating in the air and in water.

Where can these corpuscles originate?  Nothing is easier than the production of these germs, in spite of the presence of air in contact with septic fluids.

If abdominal serous exudate containing septic vibrios actively growing by fission be exposed to the air, as we suggested above, but with the precaution of giving a substantial thickness to the layer, even if only one centimeter be used, this curious phenomenon will appear in a few hours.  The oxygen is absorbed in the upper layers of the fluid—­as is indicated by the change of color.  Here the vibrios are dead and disappear.  In the deeper layers, on the other hand, towards the bottom of this centimeter of septic fluid we suppose to be under observation, the vibrios continue to multiply by fission—­protected from the action of oxygen by those that have perished above them:  little by little they pass over to the condition of germ corpuscles with the gradual disappearance of the thread forms.  So that instead of moving threads of varying length, sometimes greater than the field of the microscope, there is to be seen only a number of glittering points, lying free or surrounded by a scarcely perceptible amorphous mass. [Footnote:  In our note of July 16th, 1877, it is stated that the septic vibrio is not destroyed by the oxygen of the air nor by oxygen at high tension, but that under these conditions it is transformed