Then, in the most honourable manner, the doctor hastened to state, in a communication to the Academy of Sciences, that he regretted doubly not having known about splenic fever the year before, as he might have been able, on the one hand, to diagnose the formidable complication which had manifested itself in the woman who died on April 4, 1878, and, on the other hand, to have traced out the mode of contamination which now eluded him. He had, however, succeeded in learning a few details regarding the unhappy woman. She was a charwoman, and lived in a little room adjoining the stables of a horse-dealer. Through these stables a large number of horses passed continually. But to return to our septic vibrios. If air destroys them, if their culture is impossible in contact with air, how can septicæmia exist, since air is everywhere present? How can blood exposed to the air become septic from particles of dust on the surface of objects or which the air holds in suspension? Where can the septic germs be formed? The objection seems a serious one, but it disappears before a very simple experiment. Take some serum from the abdomen of a guinea-pig which has died of acute septicæmia. It will be found full of septic vibrios in process of generation by fission. Let this liquid be then exposed to the contact of air, with the precaution of giving a certain depth to the liquid--say, a centimeter of depth. In some hours, if examined with the microscope, the following curious spectacle will be witnessed: In the upper layers the oxygen of the air is absorbed, which is manifested by the already changed colour of the liquid. There the filamentous vibrio dies, and disappears under the form of fine amorphous granulations deprived of virulence. At the bottom of this layer of one centimeter in thickness, on the contrary, the vibrios, protected from the approach of oxygen by those of their own kind which have perished above them, continue to multiply by fission until by degrees they pass into the state of spores; so that instead of moving threads of all dimensions, the length of which sometimes even extends beyond the field of the microscope, nothing is now seen but a dust of brilliant isolated specks, upon which the oxygen of the air has no action. It is thus that a dust of septic germs can be formed even in contact with air. And thus it becomes possible to understand how anaerobic organisms may be sown in putrescible liquids by the dust suspended in the atmosphere. Thus also may be explained the permanence of putrid diseases, even of those which are caused by anaerobic microbes, that cannot live in the atmosphere and which escape destruction by becoming spores.