ATROPHY, DEGENERATION, PIGMENTATION. AND XECROSIS. 



hard and brown or black mummification, or dnj gangrene. ' On the other 

 hand it may, when putrefactive bacteria are present, in addition to its 

 discoloration, become soft and infiltrated with foul-smelling gases motet 

 gangrene. If the affected part be comparatively bloodless, the discolor- 

 ation, which is largely due to decomposition of the blood pigment, may 

 be absent. 



FOCAL NECROSIS. Necrosis involving a small circumscribed area of 

 tissue, such as is frequent in toxaemia, is called focal necroste, p. 201. 



ULCER ATION. Necrosis with erosion involving the surface of the 

 skin or of the mucous or serous membranes is called an nicer. An ulcer 

 may be necrotic in origin, from the cutting off of nutrition in a circum- 

 scribed area, as in some forms of gastric ulcer. This may be associated 

 with reactive inflammatory processes which tend to promote repair. On 

 the other hand, the process may be inflammatory in origin, death of tis- 

 sue following. 



COAGULATION NECROSIS. If dead areas of tissue (whether this con- 

 dition be due to mechanical injury, to disturbances of nutrition, or to 

 the local action of bacterial or other poisons) contain the substances 

 necessary for the coagulation of their albuminous constituents, or if they 

 be bathed with body fluids from adjacent parts in which the circulation 

 is maintained, a characteristic coagulation 

 of the uecrotic elements is apt to occur. 

 The composition of the cells of the tissue 

 is altered, so that the cell bodies are shin- 

 ing and translucent, sometimes altered in 

 shape ; while the chromatin and finally the 

 nuclei of the cell disappear (Fig. 28). 

 The whitft_iiifg,ro.tinii&-.nf the spleen H"d 

 kidneys, the areas of coagulation necrosis 

 in tuberculosis^ and the pellicle in croupous 

 inflammation of the mucous membranes are 

 ttannosTconimon examples of this lesion. 



If, for example, in the spleen, one of 

 the small arteries is plugged by an embolus, 

 a corresponding portion of the spleen be- 

 comes anaemic and appears as a white, 

 wedge-shaped mass, sharply defined from 

 the surrounding splenic tissue. If such a 



' The disappearance of the chromatin white infarction has existed but a Short, 



from the nuclei is indicated by their fail- time there is hardly any difference between 



ureto^especiany marked in the up- ^ appearauce of ^ ts anatomical element* 



and those of the surrounding spleen, ex- 

 cept that they are differently affected by stainiug-fluids. If the infarc- 

 tion is older, the cells are small and shiny and their nuclei cannot be 

 seen. 



In croupous inflammations of mucous membranes the epithelial cells 



'For a study of senile gangrene see Falta, Zeitschr. f. Heilkunde, Bd. xx., p. 393, 

 1899, Bibl. 



FIG. 38. COAGULATION- 

 CELLS. 



