242 PASTEUR: THE HISTORY OF A MIND 



After Pasteur, Cohn had studied the mode of formation 

 and the resistance of these spores in Bacillus subtilis, and 

 had put forth the hypothesis that the bacteria of an- 

 thrax possibly behaved like this bacillus. But none 

 of these precedents detract in the least from the merit 

 of Koch: it was he who showed the r61e of the spore in 

 the etiology of anthrax, and he did it in a way truly mar- 

 vellous for its simplicity. 



If one places in the thermostat or even leaves exposed 

 to summer heat a drop of fresh beef-blood serum or of 

 the aqueous humor of the eye, sown with a very small 

 fragment of fresh spleen from a mouse affected with 

 anthrax, a microscopical examination at the end of 

 15 to 18 hours shows the following appearances: in the 

 center of the slide which covers the preparation, where 

 the air cannot penetrate easily, the bacilli are in their 

 original state and have not elongated. Half way, from 

 the edges of the cover-glass the bacilli are longer, twisted 

 and bent and so much the more elongated as they are 

 nearer the margin. Certain ones, those which are most 

 hi contact with the outer air, contain typical spores, 

 sometimes arranged regularly in the filament like beads 

 (Fig. 20, left side). Ultimately these free themselves 

 from the envelope in which they are formed. They 

 are then disseminated through the liquid like an amor- 

 phous powder. But this dust is living, for, if transferred 

 to a new drop of serum, there spores produce at the end 

 of 3 or 4 hours new bacilli, capable, like the first, of 

 causing the death of the animal inoculated with them. 

 There is then no diminution of virulence in passing 

 through the spore state. 



We see that Koch, passing over and beyond Davaine, 

 who had not thought of it, was not satisfied to repeat 

 Delafond's cultural experiments. He succeeded in the 

 first attempt in doing that which Delafond had tried 



