THK Ri:TirT"I.()-KNT)()TnKrJ.\r. SYSTE^L 95 



Phagocytosis. — Botli iiiaerophagcs and niicropliagcs have to ])c 

 considered in any discussion of pliagocytosis. From the stand- 

 point of the defense of the body against disease the engnlfment 

 of bacteria or other infectious agents by amoeboid cells raises the 

 following three important questions: (1) How do the phagocytes 

 and the bacteria get together? (2) What is the mechanism of 

 engulfment? (3) What disposition is made of the engulfed 

 organisms ? 



It would seem evident that tlie fixed histiocytes, as e.g., the 

 Kupffer cells of the liver, are concerned with the removal of bac- 

 teria and other substances brought to them by the circulation while 

 the free histioc^'tes and neutrophiles can he mobilized wherever 

 needed. The mechanism of mohilization has been investigated 

 quite extensively. It is known that many substances, among them 

 bacterial protein, attract phagocytic cells. This is called positive 

 chemotaxis. When phagocytes are repelled it is called negative 

 chemotaxis. Attention is called in Chapter III to Menkin's dis- 

 covery of a leucocyte-attracting .substance in inflammatory ex- 

 udates. He has obtained this nitrogenous substance in crystalline 

 form and named it "leukotaxine." It is thought that amoeboid 

 cells move toward the source of a chemotactic substance because 

 of the change that the latter substance effects in the surface tension 

 of the phagocyte. Among other theories offered in explanation of 

 the observed attractions of phagocytes are that osmotic forces 

 govern their movements, that the difference in the surface potential 

 between the amoeboid cell and the bacteria is the important factor 

 in chemotaxis. 



IMenkin seems to have shown that the hydrogen ion concentration 

 is an important factor in determining the prevailing type of cell 

 in an area of inflammation although it is not the chemotaxie factor. 

 Apparently there is no theory that explains adequately the 

 mechanism of attraction or tropism of free amoeboid phagocytic 

 cells in the body. In an interesting report by Mallery and Mc- 

 Cutcheon (1940) they say that the motility of leucocytes obtained 

 from acutely ill individuals may not only be diminished but the 

 leucocytes show a less direct approach to the bacteria. 



In regard to the factors that play a role in the engulfment of 

 bacteria by phagocytic cells Mudd (1927), as well as others, thinks 

 that the presence of a film of denatured globulin on bacteria or 



