Louis Pasteur: His Life and Labours

by René Vallery-Radot

On April 30, 1877, Pasteur read to the Academy of Sciences, in his own name and in that of his fellow-worker, a note in which he demonstrated, this time in a completely unanswerable manner, that the bacilli called bacteria, bacterides, filaments, rods, in a word the bacilli discovered by Davaine and Rayer in 1850, constituted the only agent of the malady.

A little drop of splenic fever blood, sown in urine or in the water of yeast, previously sterilised—that is to say, rendered unputrescible by contact with air free from all suspended germs—produces in a few hours myriads of bacilli or of bacteria. A little drop of this first cultivation sown in a second flask containing the same liquid as the first and prepared with the same precautions as to sterility and purity, shows itself no less fertile. Finally, after ten or twenty similar cultures the parasite is evidently freed from the substances which the initial drop of blood might carry with it; yet, if a very small quantity of the last culture is injected under the skin of a rabbit or a sheep, it kills them in two or three days at most, with all the clinical symptoms of natural splenic fever.

It might be objected that the parasite was associated in the cultivating liquid with some dissolved substance that it had produced during its life and which acted as a poison. Pasteur accordingly transported some cultivating tubes into the cellars of the Observatory, where a temperature absolutely constant reigned, a circumstance which permits of the deposit of all the parasitic filaments at the bottom of the tubes. Inoculating afterwards both with the clear upper liquid and with the deposit at the bottom, he found that the latter alone produced disease and death. It is, then, the bacteria which cause splenic fever. The proof was given and no further doubt remained.

I.

Yes, splenic fever is no doubt produced by bacteria just as itch is produced by acaries and trichinosis by trichinæ. The only difference is that the parasite of splenic fever can only be seen by means of a rather powerful microscope. Here, then, is a disease in the highest degree virulent, due in its first cause to the infinitely little. Pasteur laid hold of and isolated this terrible virus. It was in a microscopic parasite, and in it alone, that the virulence of splenic fever resided. A great scientific fact had been gained. A virus might consist not of amorphous matter, but of microscopic beings. The virulence was due to their life.

Liebig, and all the chemists and doctors who had accepted and maintained his doctrine, totally repudiated all vital action in fermentation as well as in contagious and infectious diseases. Dominated by their hypotheses, they allowed themselves to be deceived by false assimilations to facts of a purely chemical kind, which appeared to them to be connected with the phenomena of fermentation and virulence.

Liebig wrote, 'By the contact of the virus of small-pox the blood undergoes an alteration, in consequence of which its elements reproduce the virus, and this metamorphosis is not arrested until after the complete transformation of all the globules capable of decomposition.'

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. Nothing is more striking than the rapid inflation and almost immediate putrefaction of animals which have succumbed to splenic fever. Of all the vibrios ready to pass from the intestinal canal into the network of mesenteric veins which surround the canal those which seem to take the foremost place are the septic vibrios. These specially merit the name of vibrios of putrefaction, from the very putrid gases which result from their action upon nitrogenous and sulphurous substances. The others diffuse themselves more or less slowly in the blood, but the septic vibrio takes almost immediate possession of the dead body. Already after twelve or fifteen hours, the blood of the diseased animal, which at the time of its death and during the first following hours contained exclusively the parasite of splenic fever, harbours at one and the same time both the bacillus of splenic fever and the septic vibrio. Then occur the very curious effects arising from the anaerobic nature of these vibrios, and their opposition to the bacillus of splenic fever, which is exclusively aerobic. Diffused in blood deprived of oxygen gas, the splenic bacillus soon perishes. In its place are to be found amorphous granulations deprived of all virulence. The septic anaerobic vibrio, on the contrary, finds itself after death in the most favourable conditions for its life and development. Not only does it penetrate into the blood by the deep mesenteric veins, but also into the liquids which ooze out of the abdomen and muscles.