SEVENTH PART 

 STUDIES ON THE ETIOLOGY OF MICROBIAL DISEASES 



I 

 THE IDEAS ON CONTAGION PRIOR TO 1866 



We have reached the period when Pasteur, who had 

 his eyes fixed for a long time upon the promised land 

 of pathology, was going finally to be able to enter it. He 

 was ripe for this work, and provided with the necessary 

 technical outfit to undertake it. His laboratory was 

 at that time the only one in which it was possible to 

 properly handle bacteria and be certain of the purity 

 of a sowing carried through an indefinite series of suc- 

 cessive cultures. While elsewhere every one was strug- 

 gling with nutrient liquids of mediocre composition 

 such as those mineral solutions of Pasteur or of Cohn, 

 which have played so many tricks with Klebs and those 

 who made use of them, Pasteur had discarded them for 

 a long time, and had adopted the fertile principle of 

 giving to each bacterium the kind of medium adapted 

 to it. 



It was following the beautiful researches of Raulin 

 that he had understood the importance of this question. 

 He had reflected for a long time and he called the atten- 

 tion of his pupils frequently to the fact that when 

 cultivated upon its favorite medium, the discovery of 

 which had given Raulin so much trouble, Aspergillus 

 niger defends itself unaided and successfully against the 

 intervention of every parasite. While one is obliged 

 to operate protected from the germs of the air and in 



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