ACTIVE AGGRESSIVITY 43 



strated by injecting two aggressin-immune animals, A and B, 

 intraperitoneally with equal doses of a suitable number of organisms, 

 A receiving, in addition, a certain amount of aggressin. After the 

 lapse of one or two hours the peritoneal fluid of B can then be shown 

 to contain large numbers of leukocytes, and at the expiration of four 

 hours the exudate is thick, tenacious, milky looking, and is composed 

 almost entirely of polynuclear leukocytes which have taken up many 

 or all of the injected organisms according to the number which were 

 originally introduced. In A, on the other hand, the fluid is abundant, 

 relatively clear, poor in cells, but swarming with organisms, few if 

 any of which have been disposed of by phagocytosis. Bail's explana- 

 tion is that in B, where no aggressins have been injected, there was 

 nothing to prevent the immediate inroads of the leukocytes, which 

 was facilitated in fact by the immune condition of the animal, any 

 aggressins that were formed by the bacteria being bound by the 

 antiaggressins already present. In A, on the other hand, the anti- 

 aggressins were neutralized by the extra injection of aggressins as 

 such, which, moreover, in the presence of bacteria, exercised their 

 negatively chemotactic influence upon the leukocytes, so that 

 bacterial development could go on undisturbed. 1 



This interpretation seems quite adequate to explain the function 

 of the aggressins in infections with those organisms which are 

 notoriously subject to phagocytosis, and in which other destructive 

 agencies on the part of the invaded animals play no role. As will 

 be shown in detail in Chapter VI, there are infections, however, as 

 with the cholera vibrio, for example, in which phagocytosis only plays 

 a subordinate role, but in which the destruction of the organisms is 

 brought about through certain bactericidal substances (bacteriolysins) 

 which are present in the serum. In such cases it is at first sight 

 difficult to see how the aggressins can play a role at all, if, as Bail 

 suggests, their influence is directed almost entirely against the 

 leukocytes. He has pointed out, however, that this is the case, 

 nevertheless, for it can be shown that the leukocytes are capable of 

 rendering harmless the so-called endotoxins which are liberated dur- 

 ing the dissolution of the bacteria (in consequence of the bactericidal 

 sc. bacteriolytic property of the serum), and that by preventing the 



1 It is noteworthy that the aggressins by themselves are not negatively chemo- 

 tactic, but excite hyperleukocytosis. 



