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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 inextin- 

 guishable 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 Eussian 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 de- 

 populated 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. Eochard, in a report to the Acade*mie de 

 Me"decine, 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. 



" The most decisive of all the proofs which can be invoked 

 in favour of the possible correlation between a determined 

 affection and the presence of a micro-organism, is that afforded 



