276 PATHOLOGY OF NUTRITION. 



ucts. Macroscopieally the affected area is pale, opaque, waxy, 

 and, later, gray in appearance. On mucous surfaces a false 

 membrane is formed, as seen in diphtheria. 



In liquefaction-necrosis there is a kind of peptonization of 

 the tissue-elements, which break down and become fluid, the 

 active agent being some bacterial or non-bacterial ferment. 



The term caseation is used to describe a degenerative change 

 where the tissue macroscopically has the appearance of hard 

 or soft cheese, and is most frequently seen in connection with 

 tubercular and syphilitic inflammations. Microscopically one 

 finds simply a fine granular debris. 



Fat-necrosis is a variety which affects fatty connective 

 tissues. It is most frequently noted in the abdominal cavity 

 in the subperitoneal fat, and generally is associated with 

 some pathological change in the pancreas. It is character- 

 ized by the formation of opaque, white areas about the size 

 of a pea. Microscopically the cell-contents are crystalline, 

 opaque, or granular (Fig. 111). 



Gangrene is the death of tissue en masse. There are two 

 varieties, dry or mummification and moist or sphacelus. The 

 former occurs when the part is so situated that rapid evapora- 

 tion of the fluids present takes place, especially when the 

 necrosis has been caused by interference with the blood-supply. 

 The latter occurs where evaporation is hindered and where 

 the blood reaching the part cannot escape owing to venous 

 obstruction. The presence of moisture favors the multiplica- 

 tion of micro-organisms, resulting in putrefactive changes, the 

 tissue becoming dark brown or a mottled greenish-black in 

 color (due to disorganized blood-pigment), and distended with 

 gases produced by the organisms. 



The Infiltrations and Degenerations. 



Though theoretically there is a difference between a degene- 

 ration and an infiltration the former indicating a conversion 

 of the cell-protoplasm into a less highly organized substance, 

 rendering it less suited for the performance of its functions, 

 while in the latter there is a substitution or deposit of some 

 new substance in the cell practically it is often difficult to 

 distinguish between the two. 



