206 Chapter VII 



The facts and views analysed in these two chapters afford us a 

 general picture of the phenomena exhibited in natural immunity 

 against micro-organisms. The dominant feature is represented by 

 the phagocytic reaction that is observed throughout the animal 

 series and that is exercised against parasites belonging to all the 

 microbial groups. Phagocytosis is exhibited not only by the macro- 

 [2i7]phages but also, in a high degree, by the microphages which stand 

 out as the defensive cells par excellence against micro-organisms. 

 Their action is divided into a series of vital physiological acts, such 

 as sensitiveness to the micro-organisms and their products, amoeboid 

 movements which serve to ingest the micro-organisms, and into 

 chemical and physico-chemical processes, such as the destruction and 

 digestion of the devoured organisms. 



The phagocytes enter into a struggle against the micro-organisms 

 and rid the animal organism of them without requiring any previous 

 help on the part of the body fluids. Phagocytosis, exercised against 

 living and virulent micro-organisms, is sufficient to ensure natural 

 immunity. The bactericidal power of the serum, which for a long 

 time served as the basis for a humoral theory of immunity, represents 

 merely an artificial property, developed in consequence of the setting 

 free of the microcytase of the leucocytes that have become disinte- 

 grated after the blood has been drawn. The agglutinative power of 

 the normal fluids of the body plays no important part in natural 

 immunity. 



The phagocytes, in order to fulfil their function, can attack 

 micro-organisms that are capable of producing toxins. Any anti- 

 toxic action against these bacterial poisons is in no way necessary 

 to allow of phagocytosis coming into action. 



Taken as a whole, the data collected on natural immunity against 

 micro-organisms clearly demonstrate that the destruction of these 

 parasites in the refractory animal organism represents merely a special 

 phase of the resorption of formed elements. 



