382 RETROGRESSIVE CHANGES 



by bacteria, and Ruppel '" found that the tubercle bacillus produces 

 substances precipitating- proteins ; hence coagulation necrosis in bac- 

 terial infections may be brought about in this way, and SchmoU "^ 

 has shown that the necrosis occurring in tubercles is associated with 

 an almost complete coagulation of the cell-proteins. 



Necrosis associated with infiannnatory exudation is, of course, ac- 

 companied by coagulation of the fibrinogen of the exudate (e. g., 

 diphtheria) ; this type of coagulation necrosis is chemically a simple 

 Mbrin-formation and readily understood. The peculiar hyaline de- 

 generations of parenchymatous cells {e. g., Zenker's degeneration 

 of muscles) are often included under this class, but it would seem 

 more probable that the processes consist rather of the fusion of the 

 structural elements of the cell into a homogeneous substance than a 

 true coagulation. When necrosis is produced by chemical means 

 more or less coagulation of some of the soluble proteins probably 

 takes place ; even in plant cells this coagulation of dead protoplasm 

 is described.'- 



Liquefaction necrosis occurs particularly in the central nervous 

 system, where the cell substance seems not to undergo the coagula- 

 tive changes described in the preceding paragraphs. Whether this is 

 due to a lack of tissue-coag-ulins or to a difference in cell composition 

 cannot be said, but the large proportion of lipoids in brain tissue is 

 probably an important factor. Probably "edema ex vacuo" is re- 

 sponsible for much of the accumulation of fluid, due to the anatomical 

 conditions that prevent a shrinking or collapse of the tissues to fill 

 in the gap, and the lack of connective-tissue formation. Aseptic 

 softening in general may be safely ascribed to digestion of proteins 

 by cellular enzymes, either from the dead cells or from the leuco- 

 cytes. Suppuration is merely a form of liquefactive necrosis, in 

 which such digestion is particularly rapid because of the large num- 

 ber of leucocytes that are present. Necrosis of the gastric mucosa or 

 of the pancreas is also followed by rapid liquefaction, through the 

 action of the digestive enzymes of these tissues. When necrosis is 

 accompanied by edema (as in superficial burns), the fluid enters the 

 cells in large amounts, and in this way another form of liquefaction 

 necrosis may be produced. Bacterial enzymes may be a factor in pro- 

 ducing liquefaction of dead tissues, but with most pathogenic foinns 

 there is little proteolytic activity. ^^ 



Caseation. — This term is applied to a form of coagulation necrosis 

 in which the dead tissue has an appearance quite similar to that of 

 cheese. If we bear in mind the fact that cheese is a mixture of 

 coagulated protein and finely divided fat, and that in caseation we 



ToZeit. phvsiol. Cliem.. 1898 (26), 218. 



71 Dent. Arch. klin. Vvd., in04 (81), lt!.S. 



■^ (laiaukov, Zcit. clioni. Kolloide, 1!»1() (fi), ^(in ; l.op.'sclikin. Bor. DcMit. Bot. 

 (Jesell., 1012 CM)), .')28. 

 ■ 73 See Bittrolff, Beitr. path. Anat., 101.') (fiO), X^7. 



