CHAPTEE II 

 PHAGOCYTOSIS 



The studies in immunity which have been outlined 

 in the preceding chapter have dealt entirely with the 

 phenomena occurring in the reaction between bacteria 

 or bacterial products and the body fluids. These 

 studies have formed the basis of a theoretical concep- 

 tion of immunity formulated chiefly by the German 

 school of bacteriologists. Parallel with these develop- 

 ments, however, investigations on immunity have 

 been carried on which have brought to light many 

 important facts concerning the participation of the 

 cells of the body in its resistance to infectious 

 organisms. The phenomenon which Metchnikoff and 

 his pupils at the Pasteur Institute have studied in 

 great detail, and upon the occurrence of which they 

 have based their conception of immunity, is known as 

 ** phagocytosis." 



It is well known that among the lowest unicellular 

 animals the nutritive process consists in the ingestion 

 of minute particles of organic matter by the cell. If 

 the ingested particle is of an inorganic nature and 

 indigestible, it will again be extruded after a varying 

 time. If, however, the ingested substance is of a 

 nature which can be utilised in the nutrition of the 



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