INFLAMMATION. 103 



Those concerned are capable of independent move- 

 ment, and make their exit from the capillaries by 

 insinuating themselves between the cells which line 

 the capillary walls. The fenestra which they open 

 close again, but not quickly enough to prevent the escape 

 of a few of the red cells. Once beyond the vessel- 

 walls the movements of leucocytes are determined by a 

 mysterious force exerted by the infectious agents. 

 This force (chemotaxis) either attracts (positive chemo- 

 taxis), or repells them (negative chemotaxis). 



Negative chemotaxis, however, is only 

 Chemotaxis. active so long as the agent is present, for 



on the cessation of the agent's action, or 

 its elimination, leucocytes return and take up their 

 specific functions. In inflammatory conditions the 

 leucocytes have several offices to perform; they carry 

 off the debris of injured cells, and any foreign matter 

 introduced when the injury was sustained; they also 

 destroy by digestion invading bacteria; a third ofhce 

 is to take part in the formation of new tissue. In the 

 last instance they are actually converted into grow- 

 ing tissue cells. Metchnikoff, a distinguished bacteriol- 

 ogist, who is our greatest authority on the place of 

 leucocytes in inflammation, contends that they are also 

 largely concerned in the production of immunizing 

 substances (antibodies). Be this as it may, it is plain 

 that the leucocytes are exceedingly valuable factors 

 in inflammations. 



