This vague theory of viruses was forced to give way before the multiplied experiments of Pasteur. But before occupying himself with further discoveries, although it had been irrefutably proved that the microscopic parasite was the true contagium, it was necessary to throw light upon the facts, mainly accurate, which had been announced by Jaillard and Leplat, and to bring them into harmony with the facts, not less certain, which had been advanced by Davaine. The rabbits which Jaillard and Leplat had inoculated with a drop of the blood of a cow or sheep stricken with splenic fever, died rapidly, and the blood of these rabbits was shown to be also virulent. It was sufficient to inoculate other rabbits with a very minute quantity to cause their death. But Jaillard and Leplat affirmed that the examination of that blood did not reveal the existence of any microscopic organisms. Paul Bert, on his part, had succeeded in destroying the bacteria by compressed oxygen, and yet the virulence had continued. Were there, then, two kinds of virus? What escape was there from this darkness? A new light suddenly began to dawn. Pasteur had already some years previously demonstrated that the animal body is sealed against the introduction of lower organisms--that in the blood, the urine, the muscles, the liver, the spleen, the kidneys, the brain, the marrow, and the nerves, in a normal state, no germ is found, or particle of any kind, known or unknown, which could be transformed into bacteria, vibrios, monads, or microbes. The intestinal canal alone is filled with matters associated with a host of germs and living products in process of development, and in divers states of physiological action. Not only is its temperature favourable to the life of infusoria, but it receives incessantly matters charged with the germs of these microscopic organisms. To the upper portions of the canal the air still has access, so that even in the stomach aerobic microbes may be found, but in the lower parts of the intestinal canal oxygen is absent, and only anaerobic microbes can be developed there. Although the life exerted in the mucous surface of the intestines opposes itself to the passage of those little organisms into the interior of the body, this ceases to be the case after death. There is no longer any obstacle to arrest or prevent them from acting according to the respective laws of their evolution and of the decomposing influence which belongs to them. It is by anaerobic organisms, in fact, that the putrefaction of dead bodies is begun. They penetrate into the organs and into the blood as soon as this liquid is deprived of oxygen; and it is not long before this happens, the oxygen fixed in the globules being soon consumed. In the body of an animal which has died of splenic fever, putrefaction is still more rapid, because, through the action of the disease, the blood is already in a great degree deprived of oxygen at the time of death.