These experiments, curious as they were, were only, so to speak, laboratory experiments. It was necessary to investigate what happened in the open country with all the variations of dryness, of damp, and of cultivation. A happy inspiration came to Pasteur and his assistants. They had buried in the midst of summer, in an isolated corner of the farm of St. Germain, near Chartres, a sheep which had died of natural splenic fever, and of which they had made the autopsy. Ten months afterwards, and again fourteen months afterwards, the idea occurred to them of collecting some of the earth from this grave. After having examined it, and established the presence of the spores of the microbe, they produced, by the inoculation of guinea-pigs, the splenic disease and death. But the circumstance which deserves the greatest attention, is that the same experiment was successfully made with the earth on the _surface_ of the grave, though this earth had not been disturbed during the interval. Some experiments were afterwards made on the earth of some trenches dug in a meadow of the Jura, where some cows which had died of splenic fever had been buried at a depth of two meters. Two years afterwards, by successive washings of the earth on the surface of the graves, deposits were extracted which at once produced splenic disease. At three trials within these two years the same surface earths produced splenic fever, while, away from the graves, the earth exhibited nothing of the kind. Finally, Pasteur and his assistants proved that on the surface of the earth which covered the buried animals, the germs were again found, after all the operations of ploughing, sowing, and reaping. But how, it will be asked, can the earth, which is so powerful a filter, allow the germs of microscopic organisms to rise again to its surface? Is one not tempted here to quote Pasteur against himself, since, in his joint researches with M. Joubert, Pasteur had proved that the waters of springs issuing from the earth, even at a shallow depth, are entirely free from germs? Such waters, nevertheless, being supplied from the earth's surface, which is constantly washed by rain, the effect must be to carry down the finest particles to the springs. But these latter, notwithstanding conditions so conducive to their pollution, remain perfectly pure. Can there be a better proof that earth of a certain thickness will arrest all solid particles, even the most minute? Nevertheless, in these experiments on splenic fever, we hear of microscopic germs, starting from the depths and coming up to the surface--that is to say, in a direction contrary to the flow of the rain. This is an enigma.