254 



VETERIXARV PATHOLOGY. 



De Sclnveinitz has described a chemic substance produced by 

 the Tubercle bacillus, as necrotic acid, which is thought to pro- 

 duce necrosis in tubercular lesions. The toxin of the diphtheria 

 bacillus produces focal necrosis in practically all tissue in an 

 individual afflicted with diphtheria. The products of pyogenic 

 bacteria produce marked tissue destruction. 



Chemic substances produce necrosis by coagulation of the 



Fig. 13:'. — Bacillus Necrophnriis — Fl. omnrphlc form. 



K 



albumin by dehydraticm or by the formation of new cell com- 

 pounds, thus inducing metabolic disturbance and cell death. 



Temperature I'linaticDis. — All active cells have a maximum 

 and a minimum temperature. Thermic variations beyond these 

 means are injurious and destructive if the variation is extensive. 

 The high temperature causes coagulation of the cell protoplasm 

 (cloudy swelling), which, if extensive, destroys the cells. 

 Necrosis resulting from burning is of common occurrence. Low 

 temperature is not as rapidly destructive as high temperature. 

 Freezing produces necrosis of the tissues of warm blooded ani- 

 mals, probably because of cell disintegration induced by the for 

 mation of ice in the cells. 



Types or Varieties of Necrosis. — Several factors may be used 

 as the basis for the classification of necrosis. 



Etioloqy. — According to the cause, necrosis may be : a. In- 

 anition necrosis, b. Thermic necrosis, c. Chemic necrosis. 



