MECHANISM OF INFECTION 77 



The " substance rat" may thus be considered like an anti- 

 gen for paratyphoid and this antigen provokes the formation 

 of an antibody exactly in the same way, and by the same 

 mechanism, as the fixing substance of the bacteria becomes 

 antigenic for the rat and produces in the organism of the 

 rat the formation of a specific antibody. 



We may assume that bacteria become pathogenic for an 

 animal species exactly in the same way as the organism of 

 these species becomes in its turn pathogenic for the bacteria. 

 The procedure which we have employed for rendering para- 

 typhoid, which is primarily pathogenic only for field mice, 

 virulent for rats does not apply only to this particular case. 



Dujardin and Beaumetz have rendered virulent, for 

 sheep and goats, a culture of pleuropneumonia which had 

 been considered as pathogenic exclusively for cattle, by 

 cultivating the bacteria of this disease in incompletely 

 digested mutton broth, and we know from Pasteur that 

 anthrax may become avirulent and may re-acquire its lost 

 virulence by passages through more sensitive animals. We 

 know that the bacillus of tuberculosis may lose its virulence 

 after a long series of passages in exclusively crystalloid 

 media, and that the tubercle germ of cold-blooded animals 

 is entirely harmless for the guinea-pig, but may become 

 pathogenic for this animal by appropriate cultures and 

 passages. 



The processes may vary for each particular case in their 

 details, but the principle ought to be a general one and 

 should apply to all living beings. The indispensable condi- 

 tion under which bacteria can become pathogenic and 

 under which an organism can produce a specific antibody 

 consists in penetration into the interior of the bacteria or 

 into the interior of the organism of a substance in colloidal 

 state, that is to say, incompletely digested, whose digestion 

 can be completed by the cell. Thus, bacteria which are 

 completely transformed into ammo-acids by gastro-intestinal 

 digestion cannot become pathogenic, nor can bacteria 

 nourished exclusively by the amino-acids split off from 

 animal albumins become pathogenic for this animal. 



The study of bacteriolysis in anthrax as well as the study 



