284 LOUIS PASTEUR. 



microbe. But a difficulty presented itself at the out- 

 set. Between this microbe and the microbe of fowl 

 cholera there exists an essential difference. The 

 microbe of fowl cholera, as is the case with a great 

 number of microscopic organisms, reproduces itself 

 only by fission. The parasite of splenic fever, on 

 the contrary, has another mode of generation ; it 

 forms spores, nothing analogous to which is found 

 in the microbe of cholera. 



In the blood of animals, as in the cultures at the 

 beginning, the splenic fever microbe appears at first 

 in transparent filaments, more or less divided into 

 segments. Up to that point, the resemblance between 

 the microbe of splenic fever and the microbe of cholera 

 is complete. But this blood, or the cultures exposed 

 to the free contact of the air, instead of continuing 

 this first mode of generation, frequently exhibit, even 

 in the course of twenty-four hours, spores distributed 

 more or less regularly along the length of the fila- 

 ments. All around these corpuscles the matter of the 

 filaments is absorbed, in the manner formerly illustrated 

 by Pasteur in the diagrams of his work on the diseases 

 of silkworms, when treating of the bacilli of putrefac- 

 tion. Little by little, all cohesion between the spores 

 disappears, and the whole collection soon forms no- 

 thing more than a dust of germs. But- and here lies 

 the great difficulty which experimenters encountered 

 in applying to splenic fever the method of gradual 



