Transformation, etc., of Pathogenic 31icrobcs. 93 



containing the residues of a culture of cholera atten- 

 uates the charboii bacillus. 



7. Attenuation by passage through the organism of 

 animals. — Pathogenic germs are subjected, by the or- 

 ganisms upon which they implant themselves, to cer- 

 tain influences of which we have already had occa- 

 sion to speak; we have noted especially the modifi- 

 cations which may supervene in the virulence of these 

 germs either in the way of increase or diminution. 



Instances of attenuation being produced under 

 these conditions are quite numerous. 



The microbe of rouget of the pig becomes well ac- 

 climated in the pigeon and the rabbit, and in these 

 two species acquires great virulence ; but, whilst the 

 organism of the pigeon renders it more active for the 

 pig, that of the rabbit diminishes its virulence for 

 this animal. This attenuation is preserved in cul- 

 tures then made in ordinary bouillon, and these cul- 

 tures can be employed as vaccine for the pig. 



The bacilli of bacteridian charbon and of symp- 

 tomatic charbon are attenuated by their passage 

 within the lymphatic sacs of the frog. 



The virus of rabies is attenuated in passing through 

 the organism of the ape to the extent of becoming 

 inoffensive for the dog and of vaccinating it. It re- 

 sults from the preceding facts that the morbigenic 

 faculty of microbes can be lessened in different de- 

 grees; in certain cases this diminution only exists for 

 those bacteria upon which the conditions determin- 

 ing the attenuation have acted, and the attenuation 

 is temporary ; in others the modification to which the 

 microbes have been subjected is more profound, more 



