I02 INFECTIOUS AND PARASITIC DISEASES. 



rounding tissues. Pain is due to tension and pressure 

 exerted on neighboring nerve-endings; heat to the 

 fact that there is both an increased amount of blood 

 in the part, and because metabohsm is locally quickened. 

 Since the nutrition of a part is obviously disturbed by 

 inflammatory phenomena, there is no need to dwell 

 on the associated disturbance of function. Dilatation 

 of blood-vessels, exudation of serum, and migration 

 of blood-cells, are therefore the body's initial response 

 to injury (local reactionary phenomena), and are pres- 

 ent in the beginning of inflammation. 



The earliest stage of inflammation, congestion, is 

 not considered beyond the borderland of health, indeed 

 it is the normal physiological state of a tissue or organ 

 when active. When, however, serum has escaped into 

 the tissues (effusion), this boundary has been passed, 

 although the part may return to normal without loss 

 of substance through absorption of the exudate by the 

 veins and lymphatics. An exudation is protective 

 to the body from infection both through its germicidal 

 powers and by dilution of toxins. 



Among the early phenomena of inflam- 

 Leucocytes. mation is the escape of cellular elements 



from the blood-vessels. These cells con- 

 sist of both red blood-corpuscles and larger colorless 

 cells, called leucocytes. There are many varieties 

 of leucocytes in the blood, but probably only two or 

 three of these have a share in the inflammatory process. 



