CHAPTER X 

 PHAGOCYTOSIS 



Historic. As Lord Lister stated in 1896, "If ever there was a 

 romantic chapter in pathology, it has surely been that of the story of 

 phagocytosis." The author of this " story" is Elie Metchnikoff. .His 

 early researches on phagocytosis in the lowly organized forms of life 

 constituted the starting-point for an entirely new series of researches on 

 the subject of Immunity, and his treatise on the "Comparative Pathology 

 of Inflammation" must ever remain a most entertaining work and a 

 medical classic. 



Several observers before Metchnikoff had considered that leuko- 

 cytes might assist in bringing about the destruction of microparasites. 

 Panum (1874) suggested that the bacilli of putrefaction might, by mak- 

 ing their way into the blood-corpuscles and being carried off to the 

 lymph-glands, spleen, etc., thus disappear from the body-fluids. Carl 

 Roser (1881) had also observed the ability of certain "contractile cells" 

 to ingest the enemy that enters the animal body. These statements, 

 however, were poorly supported by scientific data, and the subject was 

 not followed in subsequent research. As the result of zoologic studies, 

 Metchnikoff was led to discover the part played by body-cells in the 

 processes of immunity. He observed that when a food-particle arrives in 

 the vicinity of a simple unicellular organism as an ameba, the latter, 

 by reason of its "irritability, " moves forward and sends out processes of 

 its protoplasm (pseudopodia) that flow around the particle and finally 

 gather it into the interior of the cell. The particle then undergoes a 

 process of intracellular digestion, losing its sharp outline and clear ap- 

 pearance, becoming granular, and disappearing within the protoplasm 

 of its host. Similar studies were made of the processes of nutrition in 

 many unicellular animals, then through actininas, sponges, and similar 

 animals of transparent and simple organization. 



Metchnikoff was primarily a biologist, and up to this time was 

 mainly interested in the processes of nutrition in the simple forms of 

 animal life. At this stage, however, he became greatly impressed by 

 Cohnheim's description of the phenomena of inflammation. The dia- 

 pedesis of leukocytes through the walls of the blood-vessels in an 

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