136 IMMUNOLOGY 



fluencing the disappearance of living bacteria from the blood 

 stream. They interpret the general mechanism as follows : 

 "Staphylococci injected intravenously into normal rabbits circu- 

 late throughout the blood stream in large numbers, probably mak- 

 ing many passages through the organs and tissues of the body. 

 In passing through the spleen and liver, especially, conditions more 

 favorable for phagocytosis may obtain, particularly those de- 

 pendent upon slow blood flow, availability of macrophages and 

 leucocytes, mechanical conditions favoring filtration, etc. Chance 

 contacts between phagocytic cells and the relatively unchanged 

 staphylococci induce a certain degree of phagocytosis, as seen in 

 the polymorphonuclear leucocytes in the lungs and in the mac- 

 rophages and leucocytes of the liver and spleen. Eventually this 

 mechanism removes the bacteria from the circulating blood. Their 

 further fate doubtless depends upon the virulence of the micro- 

 organisms and the digestive capacities of the macrophages or in 

 other words the functional state of the phagocytes, both mac- 

 rophages and polymorphonuclear-leucocytes. As Werigo showed 

 in experimental anthrax infection, if these cells become inadequate, 

 the bacteria again multiply and generalize. 



"In the immune animals, this normal mechanism disposed of 

 the dead bacterial bodies during the preliminary period of im- 

 munization, at which time many macrophages in the liver and 

 spleen removed and digested the bacterial particles. "When at a 

 later period large numbers of living staphylococci run the gaunt- 

 let of those macrophages, there is an almost instantaneous swelling 

 of the micro-organisms, an increasing obstruction to their free pas- 

 sage through the immune liver and spleen and a tendency to clump- 

 ing of the bacteria with a resulting retention of such affected micro- 

 organisms in these organs." 



In regard to the relative importance of macrophages and neutro- 

 pliiles Cannon, Sullivan and Neckermann, state that "in such a 

 complex system, however, it is questionable whether too much 

 emphasis should l)e placed upon the comparative significance of 

 two groups of mesenchymal cells whose functions are so similar 

 and apparently complemental. " They observed phagocytosis by 

 both groups of cells. They do state, however, that the "primary re- 

 action is mainly between the cocci, immune bodies and the cytoplas- 

 mic surfaces of the macrophages, accompanied or quickly followed 



