66 ESSAYS ON BACTERIOLOGY. 



what of immtinity? If the natural process does not 

 afford it, experiment along this line would not seem 

 promising. 



Of the third class, in which both self -limitation and 

 immunity are slight or wanting, tuberculosis is a type. 

 And here the prospect in either direction seems dark. 

 "With the facts of the natural history before us, what 

 can be expected from an imitation of that process? 

 And yet the suggestion hitherto made in regard to 

 tuberculosis may be true. It may be that there is an 

 agent of self-limitation which only waits to be found 

 and isolated, which, freed from the antagonism of 

 others, may furnish an unexpected escape from de- 

 feat. Or here, and elsewhere, where the outlook 

 seems very doubtful, the facts coming in other direc- 

 tions may give light, indicating that the way to suc- 

 cess is to be sought, not in initiating the natural course 

 of events, but in utilizing agents obtained from ani- 

 mals possessing a natural immunity; by pushing fur- 

 ther the investigations upon the antagonism between 

 different bacteria, or by some means yet to be discov- 

 ered. If it is possible to cure malaria by quinine; to 

 dro^vn the yeast germ in its own secretion; to guard 

 against diphtheria or tetanus by the blood of protected 

 animals; to jugulate malignant anthrax by the harm- 

 less prodigiosus, why should it be thought impossible 

 to carry the work farther, to conquer even the great 

 destroyer, tuberculosis? 



The contest is really but just begun, and we are, as 



