252 VETERINARY PATHOLOGY. 



The term necrosis is applicable to the pathologic death of a 

 single cell, although such a limited necrosis is rarely recognized. 

 Clinically necmsis is usually not noted except when the area is 

 sufficiently large to observe with the unaided eye. 



All tissues of all animals are subject to necrosis, and it may 

 occur upon a surface or in subsurface structures. Bursattae is 

 a disease characterized by necrosis of the skin. Necrotic stoma- 

 titis, a disease in puppies, cah'cs and pigs, is accompanied by 

 necrosis of the buccal mucous membrane. Tuberculosis, glan- 

 ders, actinrim)-C()sis, and caseous-lymph-adenitis are diseases in 

 which there is surface or subsurface tissue necrosis. 



Etiology. — Necrosis may be primary but it is more fre- 

 quenth- secondary. Sec^lndar^■ necrosis is a sequel or result of 

 some otlier ]xithulogic process, as hemorrhage, oedema, throm- 

 bosis, anemia, h)-peremia, inflammation, degeneration, infiltra- 

 tiiin and infection. 



Primary necmsis is the result of; (1) obstructed nutrition; 

 (2) chemic substances; (.'"!) temperature A-ariations. 



Obstructed nutrition. — .\ tissue or part, from which nutri- 

 tion is entirel\- oi)structed, will die after all the availa1)le nutri- 

 ents have been consumed. 



Xutritif.in nia\- he oljstructed from a part by some mechanical 

 means. An occasional result of mechanically obstructed nutri- 

 tion is obser\'ed in dogs in which a rubber band has been i^laced 

 upc;n a leg, an car, the tongue, or the tail, the circulation being 

 thus obstructed tlie part distal to the rub1:ier band soon becomes 

 necrotic. The improper adjustment of bandages, especially when 

 used to support fractures, is frequently a cause of necrosis. 



Tumors, cysts, abscesses and other pathologic enlargements 

 ma\- exert sufficient pressure to obstruct circulation and jaroduce 

 necrosis. Fractures and herniae may mechanically occlude blood 

 vessels and result in necrosis. The seriousness of omental 

 hernia or, in fact, any hernia, is due to the fact that the vessels 

 supjilying the hernied structures are occluded, resulting in ne- 

 crosis and the absorption of the products of the necrotic tissue. 



The plugging of a terminal vessel by a thrombus or an em- 

 bolus (infarction) produces necrosis if collateral circulation is 

 not established. Thrombo-emljolic colic is a condition usually 

 caused primarily by the lar\ac of the Strongylus armatus enter- 

 ing and producing a parietal thrombus in the anterior mesen- 

 teric artery, fragments of the thrombus liecome detached, pass 

 down to and occlude the terminal mesenteric arteries, resulting 

 in ischemia of the walls of the intestine, and if the circulation 

 is not soon established the ischemic area becomes necrotic. 



