

384 RETROGRESSIVE CHANGES 



changes described in the preceding paragraphs. Whether this is 

 due to a lack of tissue-coaguhns 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 enzjnnes, either from the dead cells or from the leucoc3'tes. 

 Suppuration is merely a form of liquef active necrosis, in which such 

 digestion is particularly rapid because of the large number 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 producing liquefaction of dead 

 tissues, but with most pathogenic forms 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 coagu- 

 lated protein and finely divided fat, and that in caseation we have a 

 coagulation of tissue proteins associated with the deposition of con- 

 siderable quantities of fat, the reason for the gross resemblance of 

 the product of this form of necrosis to cheese is apparent. SchmolP 

 has analyzed caseous material, and found it almost entirel}" free from 

 soluble proteins or proteoses. The protein material is almost solely 

 coagulated protein, which in its elementary composition is related to 

 the simple proteins or to fibrin, and not at all to the nucleoproteins. 

 The extremely small amount of phosphorus present in the caseous 

 material indicates that the products of disintegration of the cell nuclei 

 must diffuse out early in the process. Caseation is, therefore, char- 

 acterized by a coagulation of the proteins and a dissolving outTof Jhie 

 nuclear components. Schmoll does not explain the cause of coagula- 

 tion, however. It may be that it is the same as in the coagulation of 

 anemic infarcts (since tuberculous areas are decidedly anemic), or 

 possibly the tubercle bacillus produces substances coagulating pro- 

 teins, as Ruppel states is the property of "tuborculosamin." Indeed; 

 Auclair^ claims that the fatty substance that can be extracted from 

 tubercle bacilli by chloroform is the cause of the caseation. Dead 

 tubercle bacilli do not produce true caseation, however, according to 

 Kelber;^" hence the substance causing the necrosis evidently docs not 



^ See Bittrolff, Beitr. path. Anat., 1915 (60), 337. 



8 Deut. Arch. Idin. Med., 1904 (81), 163. 



9 Arch. m6d. exper., 1899, p. 363. 



10 Quoted by Uurck and Oheindorfer, Ergebnisse der Pathol., 1899 (6), 288. 



