NECROSIS AND DEATH. 257 



tion of a substance or surface area of necrotic tissue is colli(|ua- 

 tion. Solution of the necrotic tissue is the result of enzyms 

 that dissolve or dit^est the dead tissue. Suppurative processes 

 (as abscess formation, etc.), are c.xaniplcs of this type of necro- 

 sis. Litpiefication of anemic infarcts, inflammatory exudates 

 and thrtimbi, with or without the formation of cvsts, is cidliqna- 

 tion necrosis. In the brain of horses that have died of the so- 

 called l)lind stat^'gers areas are found containing liquefied nerve 

 tissue. 



o. Caseation necrosis. — When the fluid is absorbed from li- 

 quefied necrotic tissue, the remaining solids may become cheese- 

 like, thus ]3roducing the condition known as caseation. Caseation 

 may be primary, but it is more frequently secondarv t(j li(iuefying 

 necrosis. Caseous material is granular, soft or crumbly in con- 

 sistency. Caseation is characteristic of the typical lesion of cas- 

 eous-lymph-adenitis in sheep and goats. Liquefaction precedes 

 caseation in this disease. Tubercular lesions, especiallv in the 

 bovine, is characterized Ijy caseation, although they later become 

 calcified. Necrotic centers of a caseous nature are observed in 

 the lesions of bursattae. 



4. ]\lummifying necrosis (mummification, dry gangrene). — 

 Necrotic tissues superficially located may becom.e dessicated, thus 

 producing the condition known as mummif}'ing necrosis. This 

 type of necrosis occurs upon a surface that is freely exposed to 

 air and of tissues in which there is little moisture. The ear, tail 

 and hoof lesions, characteristic of ergotism, are the most typical 

 examples of mummifying necrosis. In ergotism, the lesi(5ns are 

 produced by constriction of the arterioles. This in turn in- 

 creases blood pressure, and, consequently, the work uf the heait. 

 This ultimately results in the diminution or complete absence of 

 blood from the extremities, and the latter sooner or later become 

 necrotic. The necrotic tissue, as ears, tails, etc., in animals 

 affected with ergotism become mummified because blood is prac- 

 tically shut ofif from the afifected parts and the contained moist- 

 ure soon evaporates, for they are freely exposed to the air on 

 two or more surfaces. Frozen tissues may become niunnnified. 

 The umbilical cord in new born animals undergoes mummifica- 

 tion. 



5. Gangrene. — By the laity, the term "gangrene" is used to 

 designate any type of necrosis, and by some medical men it is 

 used to signify death of soft tissue en masse. Gangrene is that 

 type of necrosis characterized by putrefaction of the necrotic tis- 

 sue. Gangrene invariably occurs in tissues in which there is a 

 good supply of moisture, as in a tissue affected with venous con- 



