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Following Virchow, Metschnikoff stimulated many to 

 renewed efforts by his discovery of phagocytosis. He taught 

 us to regard the leucocyte as a digestive cell This view has 

 been greatly modified in recent years ; but MetschniUofTs view 

 that the leucocyte is a protective agent still holds the field, 

 though it is recognised now that it does much more than 

 simply gorge itself on bacteria. Leucocytosis may be termed a 

 protective reflex of a marvellous kind. 



Certain poisons, bacterial or chemical, and some bodies 

 other than poisons, are able, when circulating in the blood, to 

 attract the leucocytes from the marrow, their home of origin, 

 into the blood stream. These bodies may also stimulate the 

 marrow to a rapid formation of new leucocytes. 



This is the fundamental factor in leucocytosis and in 

 infective disease this knowledge can be utilized to enable us to 

 form an opinion as to the power of the body to re-act favourably 

 or otherwise to a specific bacterial poison. 



Metschnikoff as you all know believed that phagocytosis 

 is the essential feature of inflammation and the chief mechanism 

 in immunity and gave exclusively to the leucocytes and the 

 endothetial and other phagocytic cells a function of vast 

 importance. 



This view has been modified in one important particular 

 by more recent research which has demonstrated that an extra 

 cellular influence is exerted upon bacteria which is sometimes 

 a necessary preliminary to phagocytosis. 



The phagocytes have themselves the power of elaborating 

 in a large degree the bactericidal principles which assist and on 

 some occasions act as the precursor to the phagocytosis. 



Leucocytosis therefore represents Nature's attempt to rid 

 the blood and the system by means of the leucocytes and 

 their products of the bacterial and toxic causes of disease. 



In the majority of instances a leucocytosis is an abnormal 

 condition, a response to some foreign body, poisonous or other- 

 wise. In a few instances however a leucocytosis occurs as a 

 normal physiological process. To these I will briefly refer. 



