PHAGOCYTOSIS 279 



which the infected animal or human being eventually recovers. In 

 animals, furthermore, which show a high natural resistance against any 

 given microorganism, phagocytosis is decidedly more energetic than it 

 is in animals more susceptible to the same incitant. Thus, experiment- 

 ing with anthrax infection in rats, Metchnikoff was able to show that, in 

 these animals, a decidedly more rapid and extensive phagocytosis of 

 anthrax bacilli takes 'place than in rabbits and guinea-pigs and other 

 animals which are delicately susceptible to this infection. "While 

 different interpretations have been attached to this phenomenon, its 

 actual occurrence may be accepted as a proven fact. 



In his later investigations, furthermore, Metchnikoff was able to 

 show that a direct parallelism existed between the development of 

 immunity in an artificially immunized animal and the phagocytic powers 

 of its white cells. He showed that rabbits artificially immunized to 

 anthrax, responded to anthrax infection by a far more active phagocy- 

 tosis than did noi-mal, fully susceptible animals of the same species. 



It is quit.e impossible, in the space allotted, to recount the many 

 similar experiments by which the accuracy of these observations has been 

 confirmed. While few bacteriologists at the present day harbor any 

 doubt as to the truth of these contentions, the fundamental differences 

 between the conclusions drawn from these various phenomena by the 

 school of Metchnikoff and by that of the German workers may be 

 clearly stated as foUows: Metchnikoff believes that phagocytosis is 

 the cardinal factor which determines immunity, while Pfeiffer and 

 others maintain that the determining factors upon which recovery or 

 lethal outcome depends, lie in the fluids of the body, the serous exudate 

 and its contents of immune body and complement, while the phagocy- 

 tosis occurring coincidently, is merely a means of removal of the bacteria 

 after the outcome has already been decided. 



In the further developments of his theory, Metchnikoff has claimed 

 that the immune body and complement — the presence of which in 

 blood serum and exudates he by no means overlooks — are derivatives 

 of the leucocytes. 



The immune body or "fixator," as Metchnikoff has named it, has 

 been shown by Wassermann and Takaki* to be most plentiful in the 

 spleen, lymph nodes, and bone marrow of animals — all of them organs in 

 which large collections of leucocytic elements are found. Metchnikoff's 

 opinions as to the leucocytic origin of the complement, or "cytase," 



' WaKsernmnn unrl Tnkah', Bevl. klin. Woch., 1898. 



