302 THE LIFE OF PASTEUR 



by the method of cultures of organisms in a state of purity ; a 

 method by which I have solved, within the last twenty-two 

 years, the chief difficulties relative to fermentations properly 

 so called; notably the important question, much debated for- 

 merly, of the correlation which exists between those fermenta- 

 tions and their particular ferments." 



He then pointed out that if, after gathering either blood or 

 pus immediately before or immediately after the death of a 

 plague patient, one could succeed in discovering the micro- 

 organism, and then in finding for that microbe an appropriate 

 culture medium, it would be advisable to inoculate with it ani- 

 mals of various kinds, perhaps monkeys for preference, and to 

 look for the lesions capable of establishing relations from cause 

 to effect between that organism and the disease in mankind. 



He did not hide from himself the great difficulties to be met 

 with in experimenting ; for, after discovering and isolating the 

 organism, there is nothing to indicate a priori to the experi- 

 mentalist an appropriate culture medium. Liquids which suit 

 some microbes admirably are absolutely unsuitable to others. 

 Take, for instance, the microbe of chicken-cholera, which will 

 not develop in beer yeast ; a hasty experimentalist might con- 

 clude that the chicken-cholera is not produced by a micro- 

 organism, and that it is a spontaneous disease with unknown 

 immediate causes. "The fallacy would be a fatal one," said 

 Pasteur, " for in another medium, say, for instance, in 

 chicken-broth, there would be a virulent culture." 



In these researches on the plague, then, various mediums 

 should be tried ; also the character, either aerobic or anaerobic, 

 of the microbe should be present to the mind. 



" The sterility of a culture liquid may come from the presence 

 of air and not from its own constitution ; the septic vibrio, for 

 instance, is killed by oxygen in air. From this last circum- 

 stance it is plain that culture must be made not only in the 

 presence of air but also in a vacuum or in the presence 

 of pure carbonic acid gas. In the latter case, imme- 

 diately after sowing the blood or humour to be tested, a 

 vacuum must be made in the tubes, they must be sealed by 

 means of a lamp, and left in a suitable temperature, usually 

 between 30 C. and 40 C." . Thus he prepared landmarks for 

 the guidance of scientific research on the etiology of the plague. 



Desiring as Pasteur did that the public in general should take 



