260 \^ETERIN'ARV PATHOLOGY. 



dergo necrosis. In many instances, tliis occurs in the absence of 

 any circnlatnrj^ distur1)ance, indicating- that the exciting cause, 

 chemic substance, is carried by the l)lood and appears to have 

 a selective action for certain tissue. This type of necrosis is com- 

 mon in diphtheria and typhoid fever in the liuinan and in hog 

 chtilera, glanders, generalized tuberculosis and probably some 

 other infective and chemically induced diseases of the lower ani- 

 mals. 



The areas aitected are frequentlv not sufficiently large to 

 cibserve with the unaided e\'e. Alicroscopic sections show the 

 cells in various stages of necrosis. The nucleus may be appar- 

 ently normal or entirely disintegrated, the cell body may be 

 granular or h'\-aline, it may be intact or appear fragmented. Leu- 

 cocytic invasion of the necrotic area is of frecpient occurrence, 

 and may at first give the impression of an infected focus. Necro- 

 tic tissue in focal necrosis may be absorbed and the destroyed 

 tissue regenerated; it may becunie liquefied, thus forming a cyst; 

 it may become infected and be succeeded bv abscess formation, 

 or it may be substittited \\'ith scar tissue. 



4. Jack-Sr)res. — This is a name applied to a very prevalent 

 condition in jacks in which there is necrosis of the skin and sub- 

 cutaneous tissue. Perhaps jack-sores should not be classed as 

 a sejjarate or distinct type of necrosis, but it is so common that 

 it merits a special mention. The skin and su1)CUtaneous struc- 

 tures of the legs, venter surface of the abdomen and thorax, and 

 maxillary region are most frequently affected. The necrotic 

 areas may l)e very extensive, in some instances involving the 

 entire metatarsal or metacarpal region. 



The etiology of "Jack-Sores" is not known, but no doubt it 

 is the result of malnutrition and probably an irregular, indefinite 

 lynijihatic circulation is the jirimary cause. 



Tissue Affected. — No tissue is exempt fmm necrosis. The 

 tissue afl'ected depends upon the cause, the animal and o-eog- 

 raphical location. 



Disposition of Necrotic Tissue. — Necrotic tissue or products 

 derived from it are more or less irritating and may produce an 

 inflammation in tlie living tissue around the necrotic mass. 

 The i)erinecrotic infianmiatii m insures an increased number of 

 leucocytes around and in the necrotic area. The necrotic tissue, 

 leucoc}-tes and other living cells may produce enz^•ms that 

 \\ill ultimately dissol\-e the necrotic tissue. There mav be 

 a contractirin of the necrotic tissue and later it may separate 

 from the surrounding normal tissue. The reaction of the adja- 

 cent living tissue may be limited and cause the production 



