212 APPLIED IMMUNOLOGY 



varieties of bacteria have shown that they also may 

 retain their vitahty after being taken up by the leuco- 

 cytes. On the other hand, it has been shown that dead 

 bacteria are taken up and digested by the leucocytes, 

 and that insoluble foreign particles, such as carbon, 

 pigment, etc., are absorbed and deposited in parts of 

 the body where they will do no harm. It would ap- 

 pear, therefore, that this power of the leucocytes, 

 known as phagocytosis, applies to the taking up of all 

 foreign particles, irrespective of whether they are liv- 

 ing or dead bacteria, pigment, etc., thus removing 

 them from the circulation, but in itself has little or 

 nothing to do with destruction of the life of bacteria. 

 Phagocytic action is to be distinguished from the 

 bactericidal action of the leucocytes, which depends 

 upon separated soluble substances and does not take 

 place within the leucocytes themselves. 



Phagocytosis, therefore, is more or less a passive 

 endeavor to remove foreign particles from the circula- 

 tion, independently of whether they are living or dead, 

 and in this way is to be regarded as one of the de- 

 fensive forces of the organism against disease. The 

 killing and destruction of living bacteria and neutrali- 

 zation of their toxins are carried out by means of bac- 

 teriolysins, opsonins, agglutinins, and antitoxins, in 

 the soft tissues of the body, processes that are quite 

 distinct from phagocytosis. 



