PHAGOCYTIC FUNCTION OF VARIOUS TYPES OF CELLS 59 



Both types, however, are capable of taking up foreign cells when 

 these are introduced from without, although it lies in the nature of 

 their differing mobility (the granular leukocytes being essentially 

 mobile and the macrophages sessile) that the former play a more 

 important role in the actual conflict between the invading cells and 

 the defensive forces of the host. That the polynuclear neutrophilic 

 leukocytes more especially will take up bacteria and protozoa 1 has 

 been known for many years, and has been demonstrated not only 

 in vitro, but manifestly occurs also in the living body, as is sug- 

 gested by the findings in gonorrheal pus, in the cerebrospinal 

 exudate of epidemic cerebrospinal meningitis, in the peritoneal fluid 

 of general peritonitis, etc., where many of the offending organisms 

 may be found enclosed in leukocytes. 



The enormous extent to which phagocytosis of bacteria may go 

 is well illustrated by the following example which came under my 

 observation a few years ago. In a patient who was dying from 

 epidemic cerebrospinal meningitis we could demonstrate the presence 

 of meningococci directly in the stained preparation and calculated 

 their actual number to be 7,380,000 per cubic centimeter. The vast 

 majority of these were enclosed in polynuclear neutrophiles and in 

 large mononuclear cells which I was inclined to view as endothelial cells. 



The value of such forces, if they are actually directed against 

 living pathogenic organisms in the infected body, is, of course, self- 

 evident. In the earlier days of our knowledge of phagocytosis, when 

 Metschnikoff for the first time insisted upon the importance of the 

 process from the standpoint of immunity, it was argued that the 

 leukocytes were, after all, mere scavengers and could only take up 

 organisms that had already been killed by the bactericidal substances 

 of the serum (see the following chapter), and that their value as a 

 defensive force was thus merely secondary. Metschnikoff and his 

 pupils, however, have demonstrated in a series of investigations that 

 the leukocytes can actually take up living and virulent bacteria in 

 the living host. They showed this for the first time in anthrax- 

 immune pigeons where they were able to recover anthrax bacilli 

 from the leukocytes of the peritoneal exudate, both by culture and 

 animal inoculation. 



1 While this is true, generally speaking, it should be remembered that the 

 phagocytic action of the microphages is essentially directed against bacteria, 

 and that of the macrophages against animal organisms. 



