CHAPTER XVII 



OPSONINS AND PHAGOCYTOSIS 



IT was observed by Parum as early as 1874 that decay-producing 

 bacteria quickly disappeared when introduced into the body, and 

 could not be demonstrated in the blood or other tissues. To 

 Metchnikoff, however, must be given the credit of elaborating the 

 theory of phagocytosis. By the term phagocytes (Gr. phagein, to 

 eat) is meant any body-cell which is capable of taking up and 

 destroying other cells, usually those of foreign origin. These 

 phagocytes are in some cases fixed body-cells, but, for the most part, 

 are leukocytes or white blood-cells of different kinds. Upon the 

 phagocytic activity of the body-cells Metchnikoff established his 

 theory of immunity. It may be stated briefly as follows: If an 

 animal is either naturally or artificially immune to a disease, it 

 means that the invasion of the body by organisms is followed by a 

 struggle between the organisms and the phagocytes. These 

 phagocytes ingest the organisms and render them harmless. 

 Metchnikoff subdivides the phagocytes in two ways first, on the 

 basis of their morphological and functional behavior, and, second, 

 on the basis of their relationship to the surrounding tissue, i. e., 

 some are mobile, others are fixed. The leukocytes in the blood are 

 in part the free-moving phagocytes. The small lymphocytes are 

 not known to have any phagocytic power, and it is probable they 

 are not endowed with active motion. Most cells have not been 

 shown to be phagocytic. The polymorphonuclear and the large 

 mononuclear leukocytes are the phagocytes par excellence. Certain 

 fixed cells of the lymph-nodes and the spleen are likewise active 

 phagocytes. 



Metchnikoff terms the polymorphonuclear leukocytes the 

 microphages (Gr. micros, small; phagein, to eat), and the large 

 mononuclear, the macrophages (Gr. macros, large; phagein, to eat), 



