THE MECHANISM OF PHAGOCYTOSIS 189 



This, however, has never been proved, and it is entirely likely that these 

 substances are products of a general, rather than of a more restricted, 

 cellular activity, so that ultimately all immunologic processes are cellular 

 in origin. For this reason we prefer to speak of the phagocytic cell in its 

 relation to immunity when dealing with the relation and activity of mi- 

 crophages and macrophages in a limited sense in the process of phago- 

 cytosis. 



THE MECHANISM OF PHAGOCYTOSIS 



Aside from the question of whether fixed and wandering 

 cells may engulf virulent microparasites and the influence of sub- 

 stances in the body fluids upon this phase of phagocytosis, we have 

 for consideration the mechanism whereby these cells engulf bacteria 

 and other microparasites, various cells, and inorganic particles. 

 Based upon the direct observations of Metchnikoff and his pupils, 

 the phase of engulfing is accomplished by means of pseudopods 

 and the ameboid movement of the phagocyting cell, whereby the 

 particles become adherent and are finally rolled or passed into the 

 protoplasm of the phagocyte. Recent investigations by Kite and 

 Wherry 1 would indicate, however, that in so far as leukocytes are con- 

 cerned these processes are of minor importance, and that phagocytosis 

 depends upon the physical conditions of the surface of the phagocytic 

 cells, a "stickiness" of the leukocytes, whereby bacteria and other par- 

 ticles become adherent, the engulfing being a purely passive process 

 which depends upon protoplasmic streaming within the cells. They 

 believe that. such substances as opsonins act in increasing phagocytosis 

 merely because they increase the "stickiness" of the cells, and that 

 phagocytosis depends essentially upon the relative stickiness of phago- 

 cytes and bacteria; increased phagocytosis in the presence of serum and 

 particularity unheated serum is ascribed to an increased stickiness of 

 the leukocytes. Mechanical contact as well as certain variations in 

 chemical reactions may, therefore, result in the production of those 

 changes in contour and protoplasmic streaming responsible for rolling 

 the particle within the protoplasm of the cell. 



1 Jour. Infect. Dis., 1915, 16, 109. 



