196 



MICROBES AND TOXINS 



The antibodies quoted may themselves give rise to antibodies : 

 anticomplements and anti-immune bodies may be prepared. 



We know now all the factors which come into play in the 

 phenomena of immunity : on the one hand cells, the phagocytes ; 

 on the other the body fluids, containing ferments the actions of 

 which supplement each other, the immune body and the com- 

 plements ; we know also that the experiments of bacteriolysis 

 and haemolysis in vitro appear to indicate that the chief 

 phenomena of immunity are independent of the phagocytic 

 cells. Let us now examine the problem more closely and see 

 if phagocytosis stands the test brought against it by the humoral 

 theories. 



Phagocytic Immunity 



In every case in which the body possesses immunity the 

 bacteria against which immunity exists are devoured by the 

 phagocytes, which collect in crowds, incorporate, and digest 

 them. " Looked at from this standpoint immunity becomes a 

 phenomenon much more general than a mere resistance of the 

 body to infectious disease." On ultimate examination it 



reduces itself to 



h,cli 



a phenomenon of 

 cellular suscepti- 

 bility, of chemio- 

 tactic influences, 

 and of intracellular 

 digestion, Immu- 

 nity is a phenome- 

 non of digestion. 



Phagocytosis 



can be directly 



observed in many 



cases of natural 



immunity: the 



disease of Daphnia presents one of the simplest and most 



typical examples, and similar ones have been observed among 



other invertebrates. Among the vertebrates the frog owes 



Fig. 66. 



Phagocy- 

 tosis of anthrax 

 bacilli by the 

 macrophages of 

 the rat's liver. 

 (Metchnikoff.) 



Fig. 67. — Microphage of 

 the rat full of anthrax 

 bacilli. (Metchnikoff) 



