BACTERIA IN INFECTIOUS DISEASES. 243 



nounced in my first note, one sees a preparation of beer 

 yeast made exactly like one from the muscles of fowls 

 (bouillon) to show itself absolutely uusuited for the 

 cultivation of the parasite of fowl cholera, while it is 

 admirably adapted to the cultivation of a multitude of 

 microscopic species, notably to the bacteride charbon- 

 neuse (Bacillus anthracis) . 



" The explanation to which these facts conduct us, as 

 well of the constitutional resistance of some individuals, 

 as of the immunit} 7 produced by protective inoculations, 

 is only natural when w,e consider that every culture, in 

 general, modifies the medium in which it is effected ; 

 a modification of the soil when it relates to ordinary 

 plants; a modification of plants and animals when it 

 relates to their parasites ; a modification of our culture 

 liquids when it relates to mucedines, vibrioniem, or 

 ferments. 



44 These modifications are manifested and character- 

 ized by the circumstance that new cultivations of the 

 same species in these media become promptly difficult 

 or impossible. If we sow chicken-bouillon with the mi- 

 crobe of fowl-cholera, and, after three or four days, 

 filter the liquid in order to remove all trace of the 

 microbe, and subsequently sow anew in the filtered 

 liquid this parasite, it will be found quite powerless to 

 resume the most feeble development. The liquid, which 

 is perfectly limpid after being filtered, retains its limpid- 

 ity indefinitely. 



" How can we fail to believe that by cultivation in the 

 fowl of the attenuated virus, we place its body in 

 the state of this filtered liquid, which can no longer 

 cultivate the microbe ? The comparison can be pushed 

 still further ; for, if we filter the bouillon containing the 

 microbe in full development, not on the fourth day of 

 culture, but on the second, the filtered liquid will still 



