﻿STUDIES IN PLAGUE IMMUNITY. 263 



perhaps the capsules of the bacteria act in a negatively cheinotactic 

 manner. My own idea is that these organisms are negatively cheinotactic 

 for the leucocytes, but not because they possess aggressins in the sense 

 which Bail uses the term, but because they have not been changed chem- 

 ically by the action of the immune serum — that is, these bacteria have 

 either entirely escaped the action of the plague amboceptors, or a sufficient 

 portion of their receptors have not been bound to enable the leucocytes 

 to act positively cheinotactic toward them and to engulf them; the 

 phagocyte usually ingesting only the organism which has previously been 

 affected by the immune serum ; it is also possible that the encapsulated 

 organisms are not readily hydrolyzed. 



Therefore, it is obvious that in vitro the amboceptors of plague immune 

 serum unite with the receptors of the organism and that in the body of the 

 animal the process of destruction is carried on further by the phagocytes, 

 which engulf the bacteria which have been so acted upon. It is also 

 evident that the bacteria are not killed in the test tube by the immune 

 serum alone. Does the leucocyte accomplish this action, or is the 

 organism killed in the abdominal cavity by other influences before under- 

 going phagocytosis? That the latter hypothesis is not always true T 

 have been able to demonstrate by transplanting to the surface of agar 

 media loops of the abdominal exudate which contain phagocytes inclosing 

 bacteria. The organisms under these circumstances have sometimes been 

 observed to have increased within the cells and in some instances to have 

 burst the leucocyte and partially to have escaped from it. 



It therefore seems that after the bacillus has been prepared for the 

 action of the leucocyte by the immune serum, the leucocyte does play a 

 part in the digestion and ultimate destruction of the organism. On the 

 other hand, that the phagocytes in nonimmunized animals do not to any 

 extent take up plague bacilli seems equally clear and this opinion may 

 be confirmed by the study in plague infections of smears or sections from 

 plague buboes or abscesses in other portions of the body. Here, while 

 many bacteria are encountered in the endothelial cells, but very limited 

 or no evidence of phagocytosis by polymorphonuclear leucocytes is en- 

 countered. 



The destruction of the plague bacillus is then effected by the immune 

 animal in a manner partly in accord with the humoral theory of Buchner 

 and partly in accord with the phagocytic one of Metchnikoff. The action 

 of the serum in its protective effect upon the animal is neither antitoxic 

 nor bactericidal, but has been termed anti-infectious ; that is, it is a serum 

 possessed with the power of preventing infection. 



