264 PASTEUR: THE HISTORY OF A MIND 



His method was as follows: to demonstrate for the 

 septic vibrio that the return of the spore to activity 

 and to virulence does not depend on the obscure questions 

 of vital force or vital resistance, which medicine invokes 

 so readily, but that it is simply a question of the pres- 

 ence or absence of oxygen; then, when he had thus 

 smoothed the way, to marshal together and launch, 

 somewhat pell-mell, other analogous facts regarding 

 the ability of water- and soil microbes to become patho- 

 genic. Now that we know his plan of campaign let 

 us see how he carried it out. 



In the first place let us ask if "the germ corpuscles 

 of the septic vibrio, although formed in a vacuum or 

 in pure carbonic acid gas, would not need, in order to 

 become active, a small quantity of oxygen. Physiology 

 does not know to-day of any case in which germination 

 is possible in the absence of air.* So be it! nevertheless, 

 experiment has shown that the germs of the sepic vibrio 

 are absolutely inactive in contact with oxygen, whatever 

 may be the proportion of this gas; but this is always 

 on condition that there is a certain relation between the 

 volume of air and the number of germs, for the first 

 germinations, using up the air which is in solution, may 

 serve as a protection for the remaining germs, and it is 

 thus that, actually, the septic vibrio may propagate itself 

 even in the presence of small quantities of air, but not 

 if much air is present." 



That is, if, in addition to the septic vibrio, there are 

 present common aerobic bacteria,' the latter by de- 

 veloping, prepare the way for the former. Thus it is 

 that the vibrio develops in the intestinal canal, which is 

 ordinarily destitute of oxygen, and Pasteur here recog- 

 nized once more the role played by associations of bac- 



1 Rice and some other seeds are now known to germinate in this way. 

 See paper by Takahashi. Bull. Imp. Agr. Col., Tokyo, 1905. Vol. 6, 

 p. 439, Trs. 



