RETROGRADE PROCESSES 141 



Gangrene may be defined as necrosis with putre- 

 faction of the necrotic tissue. 



Dry gangrene is the form in which the tissues become 

 mummified. It occurs chiefly in parts of the body ex- 

 posed to the air, and is exemplified in senile gangrene 

 of the extremities, which is caused by failure of the 

 blood-supply to the extremities, and also in gangrene 

 which follows freezing of the extremities. 



Black Gangrene. When the gangrene has been pre- 

 ceded by congestion, the dead blood colors the necrotic 

 tissue black, giving rise to the term black gangrene. 



White Gangrene. When the part is anemic at the 

 time of death and is not afterward permeated with 

 blood, it remains pale, and the condition is called white 

 gangrene. 



Moist Gangrene. This form of gangrene occurs in 

 the presence of liquids, and, therefore, is found chiefly in 

 deep-seated tissues, as the lungs, bowels, appendix, 

 kidneys, etc. The necrosed tissue remains soft in these 

 localities and often liquefies. 



