THE INFECTIOUS DISEASES. 199 



of the polymorphoiiuclear type. These leucocytes, attracted through 

 chemotaxis, emigrate from the smaller vessels and gather iu the tissues. 

 Here they may proliferate ; through their phagocytic powers they may 

 directly or indirectly destroy living micro-organisms; by lytic sub- 

 stances which they elaborate, they may soften and remove dead tissues ; 

 or they may themselves succumb to the action of poisons or other local 

 conditions inimical to their life. While, to a limited extent, a suppura- 

 tive inflammation can be incited by chemical agents, such as ammonia, 

 turpentine, etc., in most cases it is incited and sustained by micro-organ- 

 isms or by poisons which these micro-organisms set free as the result of 

 their own metabolism or by the decomposition of substances in the tis- 

 sues or the tissue fluids. 



Before considering in detail the characteristics of the various forms 

 of micro-organisms which may act as excitants of suppurative inflam- 

 mation, it is necessary for us to survey the various phases which this 

 process presents under different conditions. 



In the first place while the emigration, proliferation, and gathering 

 of leucocytes is the most characteristic feature in this form of inflam- 

 mation, these are always associated with the accumulation of more 

 or less fluid transudate from the blood-vessels and often with the for- 

 mation of fibrin. These, the leucocytes, the serum, and the fibrin, 

 constitute the exudate. Furthermore, associated with the accumulation 

 of the exudate there may be albuminous degeneration and necrosis of 

 cells and tissue of the affected part or of the formed elements of the 

 exudate itself. Finally, a proliferation of the fixed cells of the 

 affected region frequently accompanies the exudative phases of inflam- 

 mation and may dominate the processes when regeneration and repair 

 are under way. 



Although the processes involved are esentially the same, it has been 

 found convenient to attach special names to various topographic forms 

 of suppurative inflammation, the differences depending largely upon the 

 origin, situation, extent, and complications of the primary lesion, some- 

 what, however, upon the qualities fixed or variable of the infecting mi- 

 cro-organism. Thus a suppurative inflammation involving the serous 

 surfaces and resulting in the accumulation of a purulent exudate in the 

 serous cavities, such as the pleural and the pericardial, is called empyema. 

 An exudative inflammation of the mucous membranes with a marked 

 emigration of leucocytes from the vessels of the submucosa is called a 

 purulent catarrh or blennorrhrea. 



Pustules are superficial collections of purulent exudate in the skin. 

 The result of a localized suppurative and uecrotic inflammation starting 

 usually in the hair follicles of the skin is called a furuncle or carbuncle, 

 depending upon the extent of the lesion. Ulcers in whatever way 

 originating (see p. 91) may be the seat of suppuration, the exudate 

 passing off upon the free surfaces. 



A diffuse infiltration of the subcutaneous or deep fibrous tissue or of 

 the interstitial tissue of the viscera with exudate is called phlegmon. If 



