338 INFECTION AND IMMUNITY. 



of their action is unknown, although Bail and his 

 co-workers are strongly inclined to the view that 

 they inhibit phagocytosis by some direct action of 

 the leucocytes. 



It is further interesting that immunization with 

 aggressins is said to give rise to the formation of 

 antiaggressins, and that by the use of antiaggres- 

 sive serum the action of the aggressins is neutral- 

 ized, and the bacteria consequently become the 

 prey of the leucocytes. The action of the anti- 

 aggressive serum is said not to depend on the pres- 

 ence of bacteriolysins. 



Proof of the non-identity of the aggressins of 

 Bail and the toxins produced by the organism 

 has not been very convincing. 



Investigating the resistance of virulent pneu- 

 mococci (which vary greatly from non- virulent 

 forms) to phagocytosis,, Kosenow was able, by au- 

 tolysis in salt solution, to extract the substance 

 on which this resistance depends. He was not 

 only in this way able to render them phagocytable, 

 but also by treating non-virulent strains with this 

 extract he was able to render them more virulent 

 and resistant to phagocytosis. 



The substance which he calls virulin is insoluble 

 in alcohol and ether, and is thermostable. 



