Dry Gangrene; Coagulation Necrosis. 179 



Necrosis with desiccation and shrinkage {mortiUcatio sicca, 

 mummification, dry g-ang'rene) results from deprivation of moisture 

 by evaporation, compression, chemical action or prevention of 

 the entrance of iiuids to the part. A physiological prototype is ob- 

 served in the shriveling of the umbilical cord which is converted 

 in the course of a few days after birth into a dry brown parchment- 

 like mass. On a small scale desiccation from loss of moisture may 

 be seen in the formation of crusts (eschars) on the surface of 

 wounds and ulcers, upon which usually the exuded tluid, pus, 

 extravasated blood and a portion of the underlying tissue (cutis, 

 mucous membrane) are dried up into brown or black. crusts and 

 scabs (eschars from caustics, scabs of wounds and ulcers). Mum- 

 mification of deeper and more extensive type, changing the tissues 

 into a wrinkled, brown or black, tough, leathery material, or into 

 a completely dried hard mass, may affect the extremities, ears, 

 feet, tail or quite frequently the skin, as the result of the action 

 of poisons or complete exclusion of blood from the part involved, 

 as in swine-erysipelas, ergotism or occlusion thrombosis. A com- 

 mon example of this variety of necrosis is the leather-like mummi- 

 fication which takes place in a dead fcetus retained with its amnion 

 in the uterus in case the amniotic fluid has all drained away or 

 been absorbed, putrefaction being impossible because of the absence 

 of the necessary bacteria, the fcetus becoming a veritable mummy, 

 enclosed and compressed in the uterine sac. 



Necrosis with coagulation, coagulation necrosis. Where 

 necrosed tissue assumes the character of an albuminous coagulate, 

 being changed into an elastic, dense, dull white, grayish yellow or 

 yellow, and more or less dry mass, the type of destruction i? 

 described, following Weigert, under the term coagulation necrosis 

 or sometimes caseation. This metamorphosis is peculiar in that 

 the dead area does not seem diminished or shrunken and has ap- 

 parently not suft'ered loss of its fluids, but rather tends to be some- 

 what increased in volume, projecting slightly above the surround- 

 ing structures. This swelling of the dead tissues depends upon 

 the diffusion of Ivmph from the adjacent parts through the necrotic 

 substance, saturating it. After this has taken place the coagulation 

 occurs in the same wa}- as in the formation of a blood clot, by the 

 action of an enzyme which is either derived from the necrotic cells 

 or originates from the primary cause of the necrosis. This variety 

 of necrosis is often induced by certain infectious germs (tubercle 

 bacilli, necrosing bacilli, bacilli of swine plague) which seem to 



