254 PASTEUR: THE HISTORY OF A MIND 



toward the organism in which it developed. Every 

 bacterial cell able to become pathogenic in 'any way or 

 by any means whatsoever, and thus to throw light on 

 the mechanism of the struggle with the cells of the host 

 organism, was welcome in his laboratory. 



It was for this reason that he sometimes passed so easily 

 and so rapidly from one organism to another. It was also 

 the reason why he was so indifferent to their morphology. 

 A clever and positive micrographer who came to him 

 one day and told him in very cautious language that 

 a certain microbe which he had taken for a coccus was 

 in reality a very small bacillus, was very much aston- 

 ished to hear him reply: "If you only knew how little 

 difference that makes to me." Perhaps he carried this 

 disregard of anatomical detail a little too far. But 

 his rule was to attack at once the most important things 

 and to neglect trifles. 



With his prodigious insight, he had divined at once 

 that, for the solving of these problems, he had a weapon 

 which none of his predecessors had possessed. He was 

 able, as we have said, to study, in pure culture, the 

 physiological properties of the bacteridium, or of any 

 other microbe, and to compare them in their pathological 

 reaction. In other words, he could establish the eti- 

 ology of the disease, not only by establishing more firmly 

 than had hitherto been done a relation of cause and 

 effect between the microbe and the disease, but by 

 connecting each one of the symptoms of the disease 

 with the reaction of the physiology of the micro-organ- 

 ism on that of the tissues. This was the new program, 

 which he pursued instinctively, perhaps without delib- 

 erate intention, but led by his habits of mind and the 

 trend of affairs in his laboratory. At once, he reaped 

 a harvest of discoveries. 



For example, the anthrax bacteridium is aerobic, 



