336 INFECTION AND IMMUNITY. 



which could be enumerated, provide cumulative 

 evidence of its correctness. 



AGGRESSINS 



Aggressing. Not entirely foreign to the subject discussed 

 above is the so-called aggressin theory of Bail, the 

 essential points of which may be given without 

 entering into a detailed discussion. 



Bail attributes to pathogenic bacteria the prop- 

 erty of "aggressiveness," through which they 

 directly antagonize the protective agencies of the 

 body. The micro-organisms of highest parasitic 

 powers, the "true parasites," as those belonging to 

 the hemorrhagic septicemia group, possess the 

 greatest aggressiveness, since they are able to pro- 

 liferate in the blood stream while the antibacterial 

 activities of the body (phagocytosis, etc.) are held 

 in abeyance. Other bacteria, which in causing 

 disease tend to remain localized, and, if by any 

 means they reach the blood stream, are not able 

 to proliferate greatly in this place, are "half 

 parasites" and have a lower degree of aggressive- 

 ness; they are more susceptible to phagocytosis 

 and to the action of bacteriolysins (typhoid, 

 cholera, dysentery). Saprophytes have no aggres- 

 sive action. 



This is very general, but Bail and his co-workers 

 have attempted to put the conception on an experi- 

 mental basis by demonstrating the existence of a 

 substance on which the aggressiveness of bacteria 

 depends; to this substance they give the name of 

 "aggressin." 



Intraperitoneal inoculation of the tubercle bacil- 

 lus into the guinea-pig leads to more or less 



