284 MICROBES, FERMENTS, AND MOULDS. 



microbe subsists in the blood, the inner part of the 

 organs, or merely on the surface of the digestive canal. 

 Such are the microbes of anthrax, of tuberculosis, and 

 of cholera, natural diseases which are not produced by 

 the experiments of man. Up to this time a septic 

 microbe has not been proved to be transformed into a 

 truly pathogenic microbe, and consequently a com- 

 pletely new disease, characterized by the development 

 of this microbe in the body of man or animals, has 

 not been created. 



It must also be remarked and this peculiarity is 

 common to both classes of microbes that certain 

 bacteria produce very different effects, according to 

 the animals into whose bodies they are introduced. 

 Thus guinea-pigs cannot be inoculated with the 

 experimental septicemia of rabbits and mice ; and 

 dogs and swine display more or less resistance to the 

 inoculation of anthrax. Finally, there are cases in 

 which the attempt to inoculate an animal with a 

 contagious disease merely produces a septicemia 

 which must not be confounded with it. This result 

 will not astonish those who know that some species 

 of plants, poisonous to man, can be eaten with im- 

 punity by many animals. But it is well to keep 

 this fact in mind in laboratories, when the attempt 

 is made to inoculate animals of various species. 



