286 PASTEUE: THE HISTORY OF A MIND 



determine precisely the means by which the bacteri- 

 dium passes from one animal to another, to discover 

 how the disease can be at the same time endemic and 

 epidemic, can have more or less periodic awakenings, 

 or lie dormant for long years. Koch had already out- 

 lined this subject, and Pasteur had to content himself 

 with adding the finishing touches, but these touches 

 are the work of a master. We shall be thoroughly 

 convinced of that when we note the principal facts. 

 Koch had shown how the spores are formed when an 

 animal, dead of anthrax, is buried, but he had never 

 found them in the earth, nor did he know how long 

 they lived there. Pasteur succeeded at the outset in 

 isolating the bacteridium of anthrax from the myriads 

 of germs which accompany it in the soil, always employ- 

 ing for this purpose the same method: that of pure 

 cultures in the medium best fitted to the physiological 

 needs of the anthrax bacillus. These experiments 

 date from 1881. The method of making cultures on 

 solid media, conceived by Koch, was not yet known in 

 the laboratory, having been published only that year. It 

 would certainly have simplified the problem and facil- 

 itated the researches, but we see, as has since been 

 admitted, that it was not indispensable for studies of 

 this kind, and that Pasteur extricated himself from 

 his difficulties without it. It is true that another would 

 probably have failed. 



Thanks to this method, Pasteur discovers that the 

 anthrax spores can persist a long time in the vicinity 

 of the place of burial, and that they can be found there 

 after a period of 12 years, as virulent as on the first day. 

 This gave birth to a new problem. How can these 

 spores on the soil of the burial pit resist the rain which 

 engulfs them, the wind which sweeps them away, and, 

 we should add, to-day, the light of the sun, which is more 



