Pasteur tried the effect of this microbe on guinea-pigs which had been brought up in the laboratory, and found it but rarely mortal; in general it merely caused a sore, terminating in an abscess, at the point of inoculation. If this abscess were opened, instead of being allowed to heal of its own accord, the little microbe of chicken cholera was to be found in the pus, preserved in the abscess as it might be in a phial.
“Chickens or rabbits,” remarked Pasteur, “living in the society of guinea-pigs presenting these abscesses, might suddenly become ill and die without any alteration being seen in the guinea-pigs’ health. It would suffice for this purpose that those abscesses should open and drop some of their contents on the food of the chickens and rabbits.
“An observer witnessing those facts, and ignorant of the above-mentioned cause, would be astonished to see hens and rabbits decimated without apparent cause, and would believe in the spontaneity of the evil; for he would be far from supposing that it had its origin in the guinea-pigs, all of them in good health. How many mysteries in the history of contagions will one day be solved as simply as this!!!”
A chance, such as happens to those who have the genius of observation, was now about to mark an immense step in advance and prepare the way for a great discovery. As long as the culture flasks of chicken-cholera microbe had been sown without interruption, at twenty-four hours’ interval, the virulence had remained the same; but when some hens were inoculated with an old culture, put away and forgotten a few weeks before, they were seen with surprise to become ill and then to recover. These unexpectedly refractory hens were then inoculated with some new culture, but the phenomenon of resistance recurred. What had happened? What could have attenuated the activity of the microbe? Researches proved that oxygen was the cause; and, by putting between the cultures variable intervals of days, of one, two or three months, variations of mortality were obtained, eight hens dying out of ten, then five, then only one out of ten, and at last, when, as in the first case, the culture had had time to get stale, no hens died at all, though the microbe could still be cultivated.
“Finally,” said Pasteur, eagerly explaining this phenomenon, “if you take each of these attenuated cultures as a starting-point for successive and uninterrupted cultures, all this series of cultures will reproduce the attenuated virulence of that which served as the starting-point; in the same way non-virulence will reproduce non-virulence.”
And, while hens who had never had chicken-cholera perished when exposed to the deadly virus, those who had undergone attenuated inoculations, and who afterwards received more than their share of the deadly virus, were affected with the disease in a benign form, a passing indisposition, sometimes even they remained perfectly well; they had acquired immunity. Was not this fact worthy of being placed by the side of that great fact of vaccine, over which Pasteur had so often pondered and meditated?
He now felt that he might entertain the hope of obtaining, through artificial culture, some vaccinating-virus against the virulent diseases which cause great losses to agriculture in the breeding of domestic animals, and, beyond that, the greater hope of preserving humanity from those contagious diseases which continually decimate it. This invincible hope led him to wish that he might live long enough to accomplish some new discoveries and to see his followers step into the road he had marked out.
Strong in his experimental method which enabled him to produce proofs and thus to demonstrate the truth; able to establish the connection between a virulent and a microbian disease; finally, ready to reproduce by culture, in several degrees of attenuation, a veritable vaccine, could he not now force those of his opponents who were acting in good faith to acknowledge the evidence of facts? Could he not carry all attentive minds with him into the great movement which was about to replace old ideas by new and precise notions, more and more accessible?
Pasteur enjoyed days of incomparable happiness during that period of enthusiasm, joys of the mind in its full power, joys of the heart in all its expansion; for good was being done. He felt that nothing could arrest the course of his doctrine, of which he said—“The breath of Truth is carrying it towards the fruitful fields of the future.” He had that intuition which makes a great poet of a great scientist. The innumerable ideas surging through his mind were like so many bees all trying to issue from the hive at the same time. So many plans and preconceived ideas only stimulated him to further researches; but, when he was once started on a road, he distrusted each step and only progressed in the train of precise, clear and irrefutable experiments.
A paper of his on the plague, dated April, 1880, illustrates his train of thought. The preceding year the Academy of Medicine had appointed a commission composed of eight members, to draw up a programme of research relative to the plague. The scourge had appeared in a village situated on the right bank of the Volga, in the district of Astrakhan. There had been one isolated case at first, followed ten days later by another death; the dread disease had then invaded and devoured the whole village, going from house to house like an inextinguishable fire; 370 deaths had occurred in a population of 1,372 inhabitants; thirty or forty people died every day. In one of those sinister moments when men forget everything in their desire to live, parents and relations had abandoned their sick and dying among the unburied dead, with 20° C. of frost!! The neighbouring villages were contaminated; but, thanks to the Russian authorities, who had established a strict sanitary cordon, the evil was successfully localized. Some doctors, meeting in Vienna, declared that that plague was no other than the Black Death of the fourteenth century, which had depopulated Europe. The old pictures and sculptures of the time, which represent Death pressing into his lugubrious gang children and old men, beggars and emperors, bear witness to the formidable ravages of such a scourge. In France, since the epidemic at Marseilles in 1720, it seemed as if the plague were but a memory, a distant nightmare, almost a horrible fairy tale. Dr. Rochard, in a report to the Académie de Médecine, recalled how the contagion had burst out in May, 1720; a ship, having lost six men from the plague on its journey, had entered Marseilles harbour. The plague, after an insidious first phase, had raged in all its fury in July.