182 VETERINARY BACTERIOLOGY 



peritoneal exudate is removed after the death of the animal and 

 centrifuged to remove the cellular elements as well as most of the 

 bacteria. The organisms remaining in the supernatant liquid are 

 destroyed by a chemical disinfectant. If a small quantity of this is 

 injected into a guinea-pig, together with a quantity of the specific 

 organisms that would usually be non-lethal, the animal will die' 

 with an acute infection. The injected exudate apparently makes 

 the organisms more virulent. The aggressins are contained in 

 this exudate, and convert a mild infection into one that is fatal. 

 The repeated injection of sterile aggressin causes the development 

 in the animal body of an active immunity. According to Bail, 

 antiaggressins can be demonstrated in the blood-serum of such 

 animals. One of the strongest links of corroborative evidence 

 is the fact that the bacteriolytic power of a serum in vitro is not an 

 index of the ability of the animal from which it was taken to resist 

 infection. The modus operandi of the aggressin is to be sought in 

 the inhibition of phagocytosis. Bail found that when the typhoid 

 bacillus is injected intraperitoneally, there is a marked increase in 

 the number of phagocytes in the exudate within a few hours, but 

 when they are injected with aggressin, there is no such increase 

 the phagocytes are evidently not attracted. 



This theory has not been accepted in its entirety by many 

 bacteriologists. The facts given by Bail are largely accepted, 

 but the theory is not well established. Some authors claim to have 

 shown that the so-called aggressin is simply endotoxin released in 

 the body by the lysis of the bacterial cells. It is also claimed that 

 there is no demonstrable difference between the endotoxins pro- 

 duced in culture-media and the aggressins formed in the body. 

 Peritoneal exudate containing aggressin, according to Bail, has been 

 filtered through porcelain, and found to be toxic for guinea-pigs 

 after filtration. Bail has attempted to develop practicable methods 

 of immunization in several diseases by an application of the theory. 

 None of his methods have come into general use. 



