STRUCTURAL CHANGES DUE TO DAMAGE. 313 



least resistance, until it is finally discharged along with some of the 

 bacteria and poisons. This frequently brings relief, and the abscess 

 becomes an open wound, which heals by granulations in the way 

 already outlined. 



In other cases the conflict between the bacteria and the tissues 

 may be more evenly balanced and the pus confined by granulations, 

 which are injuriously aifected on the surface, but progress toward 

 the formation of fibrous tissue in their deeper portions. Such 

 a lining of granulation-tissue is called the " pyogenic membrane" 

 of the abscess. Similar pyogenic membranes are formed on the 

 walls of sinuses resulting from the discharge of an abscess when the 

 infection is still sufficient to prevent the growth of healthy and vig- 

 orous granulation-tissue, or when the burrowing of the pus before 

 its discharge has been so slow that the granulations surrounding 

 the sinus have become organized in their deeper portions and are 

 no longer capable of nourishing young and active tissues at the 

 surface. In such a case curetting of the sinus-wall would remove 

 this imperfectly nourished tissue and promote the development of 

 vigorous granulations. 



Still another variation of the process is possible when the infec- 

 tion becomes very greatly reduced in virulence or the bacteria die. 

 In this case the granulations grow and obliterate the cavity in case 

 its contents are absorbed, leaving a puckered scar, or its contents 

 may become inspissated through absorption of the serum, and the 

 leucocytes be converted into a cheesy mass by fatty degeneration 

 combined with necrosis ; in which case the resulting mass becomes 

 encapsulated by cicatricial tissue. The resulting nodules are liable 

 to subsequent calcareous infiltration. 



3. Fibrinous Inflammation. This frequently affects the serous 

 membranes, the lung, etc. A case of lobar pneumonia may be 

 selected as a typical example. 



After a preliminary congestion of the vessels in the walls of the 

 pulmonary alveoli an exudate, consisting of serum and red cor- 

 puscles, with a comparatively small number of leucocytes, is 

 poured out into the alveoli. Here fibrin is formed, so that the 

 exudate becomes solid (Fig. 268). This constitutes the stage of 

 " red hepatization." This stage gradually passes into that of " gray 

 hepatization," in consequence of an immigration of leucocytes into 

 the fibrinous exudate, the red corpuscles meanwhile losing their 

 coloring-matter, so that the red color due to them passes into a 



