184 Necrosis. 



Ter))iiiiatwiis. Dead tissue acts upon the surrounding healthy 

 structures as a foreign body, causing both mechanical and chemical 

 irritation ; in consequence of which an inflammatory reaction is 

 uniformly established in the adjacent healthy tissues. At the 

 periphery of the necrotic part there may be observed an inflam- 

 matory zone marked by greater or less inflammatory hyperaemia 

 and accumulation of leucocytes. From the action of the fluid 

 exudates penetrating the dead tissue and of the immigrated cells 

 removing the necrotic substance, partly by liquefaction and partly 

 by phagocytosis, necrosed parts of small size may be gradually 

 absorbed, especially foci softened down into detritus and small 

 infarcts. At the site of the necrosis there is then left a space, a 

 defect, which is later filled in by proliferation of the surrounding 

 tissvie or by inflammatory scar formation. Larger necrotic areas, 

 or such as apparently cannot be softened (mummified and coagu- 

 lated portions) resist absorption; these may be circumscribed by 

 the inflammation, encapsulated or completely separated from the 

 rest of the body {demarcation, dcuiarcating iiiflammatioi, sequestra- 

 tion or circumscribed necrosis). In this way while the invading" 

 mass of leucocytes and other exudates are softening down the tissue 

 at its borders there is also proceeding an inflammatory prolifera- 

 tion of connective tissue and blood vessels (fibroblasts, angioplasty 

 and blood vessel buds) to the formation of a protective wall. If 

 the dead material be situated at the surface of the skin or mucous 

 membrane it may be sloughed ofl:' (cutaneous slough), and the 

 defect repaired either by subsequent proliferation of the adjacent 

 tissue or by cicatrization. Necrotic parts situated deeply in the 

 body are surrounded by the demarcating tissues and come to be 

 enclosed in a dense capsule of connective tissue. Dead fragments 

 of bone separated from their circulatory supply (bone splinters) 

 are enclosed by an osteoplastic proliferation of the bone marrow 

 and periosteum and thus isolated as sequestra. 



In case the gangrenous foci contain substances of toxic nature 

 the necrosis may assume a progressive character from the con- 

 vection of the toxic products of disintegration and putrefactive 

 bacteria by the invading leucocytes and lymph stream to other 

 parts. When the process is reproduced in the immediate vicinity 

 of the original focus it is spoken of as progressive necrosis or 

 gangrene ; when the putrefactive organisms are carried in the blood 

 to distant parts, causing synchronously the same processes in the 

 latter, these new foci are spoken of as secondary, metastatic gan- 



