XVII 



PHAGOCYTOSIS 

 By phagocytosis is meant a property of the leuco- 

 cytes whereby they take up into their substance 

 foreign particles, such as bacteria (see Frontispiece), 

 pigment, carbon granules, etc., thus removing them 

 from the circulation. This power belongs pre- 

 eminently to the polymorphonuclear neutrophiles, 

 though phagocytosis by lymphocytes is occasionally 

 observed. This phenomenon was discovered by 

 MetchnikofT, who regarded it as the principal if not 

 the sole means at the disposal of the body to rid itself 

 of disease-producing germs. According to his teach- 

 ing, phagocytosis included the taking up, the killing, 

 and digestion of living bacteria, as well as absorption 

 of dead bacteria and inert materials. Later studies 

 of this phenomenon have led to modification of this 

 comprehensive view by the majority of observers. It 

 has, for example, been pointed out that the absorption 

 of live bacteria by the leucocytes does not necessarily 

 lead to their destruction, and the pus of gonorrhoea 

 needs only to be cited as evidence. In gonorrhoea the 

 great majority of the gonococci lie within the leuco- 

 cytes and, far from undergoing destruction, rather 

 tend to multiplication, at the same time retaining their 

 highly infectious nature. Experiments with other 



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