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. “Since the plague is a disease,” wrote Pasteur (whose paper was a sort of programme of studies), “the cause of which is absolutely unknown, it is not illogical to suppose that it too is perhaps produced by a special microbe. All experimental research must be guided by some preconceived ideas, and it would probably be very useful to tackle the study of that disease with the belief that it is due to a parasite.