Between the years 1867 and 1870 above 56,000 deaths from a disease variously designated as “anthrax,” or “carbuncular disease,” and “splenic fever,” and in France known by the terms “charbon,” or “pustule maligne,” are stated to have occurred among horses, cattle, and sheep in one district of Russia, Novgorod, occasioning also the deaths of 528 among the human population. It occurs in two forms, one more malignant and rapid in its action than the other. In France the disease appears to be scarcely ever absent, and is estimated to entail on the breeders of cattle an annual loss of many millions of francs. As a milder epidemic it has prevailed in this country, and the disease which has lately broken out in Bradford and some other towns in the north among wool-sorters, has now been shown to be a modification of the same disease communicated by the wool of sheep that have been infected.
On examining the blood of animals, the subjects of “splenic fever,” some French pathologists had discovered the presence of certain minute transparent filaments which, by the investigations of a German physician named Koch, were proved to be a fungoid plant developed from germ particles of microscopic minuteness. By gradual extension these minute particles, termed “microbes,” attain the form of small threads or rods, to which the name of “bacilli” has been given, from the Latin bacillus, a rod or staff. These rods were found to be in fact hollow tubes, divided at intervals by partitions, which, on attaining full growth, break up into fragments, the interiors of which are found to be full of minute germs similar to those from which the rods were at first developed. These germs were found by Koch and his collaborateurs to be capable of cultivation by being immersed in some suitable organic liquid kept at a proper temperature, and the supply could be kept up by introducing even a few drops of such impregnated fluids into other fluids, and repeating the process again and again. The next step to test the potency of these germs to generate the disease in animals whence they were originally obtained, was to vaccinate animals with a few drops of the fluid thus artificially infected. Accordingly it was found that the bodies of guinea-pigs, rabbits, and mice thus inoculated became infected, and developed all the characteristic symptoms of splenic fever or carbuncular disease.
Pasteur, whose enthusiasm in the pursuit of investigations which had already been crowned with such signal success kept him awake to all that was being done by other inquirers, and made him watchful of every event that transpired relative to the epidemic diseases of cattle, was struck with the fact that some of the most fatal outbreaks of “charbon” among flocks of sheep occurred in the midst of apparently the most healthy pastures. His sagacity led him to inquire what had been done with the carcasses of animals that had died from previous outbreaks of the disease in these localities, when he found that they had been buried in the soil and often at great depths, of the same pastures. But how could the disease germs make their way to the surface from a depth of eight or ten feet? Earthworms, he guessed, might have conveyed them. And notwithstanding the incredulity with which his explanation was received, he forthwith proceeded to verify his supposition. Having collected a number of worms from the ground of the pastures in question, he made an extract of the contents of the alimentary canal of the worms, and with this he inoculated rabbits and guinea-pigs, gave them the “charbon” in its most fatal form, and proved the identity of the malady by demonstrating that the blood of the victims swarmed with the deadly “bacillus.” And here we cannot but stop to notice the remarkable confirmation that is thus given to the wonderful and beautiful observations of Darwin as set forth in his last work on “The Formation of Vegetable Mould Through the Action of Worms.” Darwin has shown beyond all dispute, as the result of his incomparable researches, that though “the plough is one of the most ancient and most valuable of man's inventions, long before he existed the land was in fact regularly ploughed, and still continues to be ploughed, by earthworms.” He has shown us that the smoothness which we admire in a wide, turf-covered expanse “is mainly due to all the inequalities having been slowly leveled by worms,” and that “the whole of the superficial mould over any such expanse has passed, and will pass again, every few years, through the bodies of worms!” It was left for Pasteur to show that these innumerable and indefatigable plowmen, whilst rendering to man such efficient service, may also be the carriers of the seeds of disease and death.
In proceeding with our brief historical account of Pasteur's and allied researches, we are arrived at the point where their analogy to Jenner's becomes manifest, and where their direct bearing on the welfare of mankind comes into view. So soon as it was known that these disease germs were low forms of vegetation, and that, like other vegetables, they could be cultivated, it was natural to ask whether, like other vegetables, their characters and properties could not be so modified as to render them at least less deleterious. Every one knows the difference between the crab-apple and its cultivated variety, the sloe and the plum, the wild and the cultivated celery. It is all the difference between unwholesome and wholesome food.
Two methods of cultivation, with a view to obtaining the desired modification of the power exercised by the bacilli and other similar germs, presented themselves, the one analogous to that really pursued by Jenner where small-pox, or the grease of the horse, was passed through the system of the cow, and then from one human being to another; and the second by carrying on the cultivation out of the living body. Both these plans have been adopted, with the result of proving that the potency of the germs can be so diminished as to render the disease produced by their introduction so mild as to be of no importance. Pasteur cultivated the bacillus in chicken broth or meat juice, and allowed a certain time to elapse before he made use of the mixture. After allowing only two months to elapse, the virulence of the germs seemed to be but little impaired, but after three or four months animals inoculated with the fluid, though they took the disease, had it in so mild a form that the greater number recovered. After a long period of six or eight months the engendered disease was so mild that all the animals speedily recovered and regained health and strength.
And now the question will naturally arise, Did animals which had passed through the mild disease thus induced acquire a protection against the original disease, if brought in contact with it in subsequent epidemics, in the same way that Jenner's vaccinated patients were protected against small-pox?
An answer in the affirmative may now be given with the utmost confidence. Experiments conducted, both in this country and abroad, by both methods of procedure, have abundantly proved that animals may be protected by inoculation so as to render them insusceptible of any form of the destructive anthrax disease.
From a remarkable paper read by Pasteur before the International Medical Congress we extract the concluding paragraph. After detailing the method pursued to obtain the requisite attenuation of the virus, and stating that by certain physiological artifices it may be made again to assume its original virulence, he proceeds: “The method I have just explained, of obtaining the vaccine of splenic fever, was no sooner made known then it was very extensively employed to prevent the splenic affection. In France we lose every year by splenic fever animals to the value of 20,000,000 francs, and even, according to one of the persons in the office of the Minister of Agriculture, more than 30,000,000 francs, but exact statistics are still wanting. I was asked to give a public demonstration at Pouilly-le-Fort, near Melun, of the results already mentioned. This experiment I may relate in a few words. Fifty sheep were placed at my disposition, of which twenty-five were vaccinated, and the remaining twenty-five underwent no treatment. A fortnight afterwards the fifty sheep were inoculated with the most virulent anthracoid microbe (or germ). The twenty-five vaccinated sheep resisted the infection, the twenty-five unvaccinated died of splenic fever within fifty hours.
“Since that time the capabilities of my laboratory have been inadequate to meet the demands of farmers for supplies of this vaccine. In the space of fifteen days we have vaccinated in the departments surrounding Paris, more than 20,000 sheep, and a large number of cattle and horses. This experiment was repeated last month at the Ferme de Lambert, near Chartres. It deserves special mention.
“The very virulent inoculation practiced at Pouilly-le-Fort, in order to prove the immunity produced by vaccination, had been effected by the aid of anthracoid germs deposited in a culture which had been preserved in my laboratory more than four years, that is to say, from the 21st March, 1877. There was assuredly no doubt about its virulence, since in fifty hours it killed twenty-five sheep out of twenty-five. Nevertheless, a commission of doctors, surgeons, and veterinary-surgeons, of Chartres, prejudiced with the idea that virus obtained from infectious blood must have a virulence capable of defying the action of what I call cultures of virus, instituted a comparison of the effects upon vaccinated sheep and upon unvaccinated sheep of inoculation with the blood of an animal which had died of splenic fever. The result was identical with that obtained at Pouilly-le-Fort—absolute resistance of the vaccinated and deaths of the unvaccinated. If I were not pressed for time I should bring to your notice other kinds of virus attenuated by similar means. These experiments will be communicated by-and-by to the public.”