122 INFECTION AND IMMUNITY. 



. Bail, discrediting the importance of the germi- 

 cidal substances of the serum for natural immun- 

 ity, assigns to phagocytosis the essential role, and 

 believes that the virulence of .the parasites depends 

 on their power to produce substances, the aggres- 

 sins, which antagonize the process of phagocytosis. 

 The aggressins were supposed to be non-toxic sub- 

 stances which were produced only in the body of 

 the infected animal. When the organisms of 

 typhoid, cholera, tuberculosis and other diseases, 

 are injected intraperitoneally into the guinea-pig, 

 the aggressins appear in the inflammatory exudate, 

 and are obtained free from living micro-organisms 

 by centrifugation and subsequent chemical sterili- 

 zation of the overlying fluid. This fluid, when 

 mixed with the homologous culture, has the power 

 of rendering fatal a quantity of the culture which 

 otherwise would be unable to produce infection, 

 and the mixture may cause a very acute death of 

 the experiment animal. Bail found all the more 

 justification for assuming the existence of this new 

 (?) substance from the fact that immunization 

 with the aggressins gives rise to a serum which 

 has the power of neutralizing the effect of the 

 aggressive exudate; hence such a serum was termed 

 an antiaggressin. 



objections. The studies of others, however (Wassermann and 

 Citron, Doerr, Sauerbeck and others) indicate that 

 the aggressins of Bail do not represent a new entity. 

 Wassermann and Citron found that the "aggres- 

 sins" as prepared by Bail are toxic, and that they 

 may be obtained in artificial cultures as well as in 

 the body of an animal. They probably represent 

 nothing more than the cytoplasm of dissolved bac- 

 teria which may exert an inhibiting effect on pha- 



