334 INFECTION AND IMMUNITY 



The numerous researches of Metchnikoff have brought out the 

 important fact that phagocytosis is regularly more active in cases in 

 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, 

 experimenting 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 infec- 

 tion. 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 im- 

 munized to anthrax, responded to anthrax infection by a far more 

 active phagocytosis than did normal, fully susceptible animals of the 

 same species. 



It is quite 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 dif- 

 ferences 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 follows : 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 phago- 

 cytosis 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 5 to be most plentiful in the 



5 Wassermann und Takaki, Berl. klin. Woch., 1898. 



