.INFLAMMATION. 125 



considerable differentiation of some of the cells has taken place, whether 

 there be a distinct circulatory apparatus or not, certain other cells are 

 left in a more primitive state: these are phagocytic and can ingest or 

 otherwise destroy deleterious material. 



When we come to man and other warm-blooded animals, it is upon 

 the leucocytes which have retained so many of the capacities of undiffer- 

 entiated protoplasm that attention is especially concentrated. It has 

 been found, as we have already seen, that the movement of leucocytes 

 may be directed toward (sometimes from) chemical substances set free 

 in their vicinity. . This chemotaxis is frequently manifested in the 

 vicinity of dead cells or tissues which are the seat of destructive me- 

 tabolism. But it is especially in relation to micro-organisms of various 

 forms that chemotaxis in the leucocytes is of the highest significance to 

 us here. 



Highly virulent micro-organisms may for a time repel the leucocytes, 

 probably through negative chemotaxis, but these may later approach 

 them. On the other hand, leucocytes most often migrate toward bacteria 

 which have gained entrance to the body. It has been proven that leuco- 

 cytes, especially the polyuuclear neutrophiles, less frequently large 

 mononuclear forms, may take into their interior and destroy living 

 bacteria. Dead bacteria also, as well as other inert material, they can 

 engulf and destroy. 



This capacity of leucocytes and other mesodermal cells eudothelia, 

 etc. to take up living bacteria and kill and digest them was persistently 

 and ably urged by Metschnikoff and his pupils as the chief protective 

 agency in the body against bacterial incursions, and to these observers 

 all the other phenomena of inflammation formerly seemed of secondary 

 importance. But it was soon shown that this extreme view is not correct. 

 For it was demonstrated by many observers that the body fluids, espe- 

 cially blood serum, is capable ot killing bacteria with which they come 

 in contact. When, however, this remarkable quality of the body fluids 

 was investigated, it was found that it is most pronounced under condi- 

 tions which involve the breaking-down of leucocytes or the liberation of 

 the destructive substances into the fluids. It was possible now to demon- 

 strate that the leucocytes do in fact contain a gerinicidal proteid sub- 

 stance or substances. These substances, which appear to be closely 

 associated with or related to nucleinic acid, have been called "alexines" 

 or "protective proteids." ' It has been further demonstrated that while 

 the eosinophile cells may move toward bacteria, they are not phagocytic, 

 but may set free granules which appear to favor the destruction of the 

 germs. 



It thus appears that the earlier view of the almost exclusive impor- 

 tance of phagocytosis is not sustained, but that even more than in the 

 action of living phagocytes the protective agencies are to be sought in 

 the body fluids. But it is also clear that the protective capacities of the 

 body fluids are the result of cell activities, as indeed might have been 

 1 For further consideration of this subject see p. 181. 



