BACTERIA IN INFECTIOUS DISEASES. 251 



particles, organic or inorganic, which come in their 

 way. And it requires no great stretch of credulity 

 to believe that they may, like an amoeba, digest 

 and assimilate the protoplasm of the captured bac- 

 terium, thus putting an end to the possibility of its 

 doing any harm. 



In the case of a pathogenic organism we may 

 imagine that, when captured in this way, it may 

 share a like fate if the captor is not paralyzed by 

 some potent poison evolved by it, or overwhelmed 

 by its superior vigor and rapid multiplication. In 

 the latter event, the active career of our conser- 

 vative white corpuscle would be quickly termin- 

 ated, and its protoplasm would serve as food for 

 the enemy. It is evident that in a contest of this 

 kind the balance of power would depend upon cir- 

 cumstances relating to the inherited vital charac- 

 teristics of the invading parasite and of the in- 

 vaded leucocyte. 



That different pathogenic organisms of the same 

 species may differ as to their power to overcome 

 the vital resistance of living animals is amply 

 proved by experiment. We have examples of this 

 in the attenuated virus of anthrax and of fowl- 

 cholera. These physiological varieties, as Pasteur 

 calls them, may be produced at will by one of the 

 methods heretofore referred to. They differ from 

 the unmodified virus in vital activity, and this is 

 especially manifested in their diminished reproduc- 

 tive power. 



In the great laboratory of nature, like causes 



