DISEASES OF THE BONES. 753 



on the withers, the diseased portion should be cut off with a fine 

 saw. Occurring in a joint, Ave must endeavor to produce anchy- 

 losis of the joint, the treatment of which has been explained as for 

 spavins, etc. 



Necrosis of Bone. 



Necrosis is generally defined to be the entire death or mortifica- 

 tion of a bone. It differs from caries, in which the bone is dis- 

 charged in particles; whereas in necrosis not unfrequently the 

 whole bone dies and becomes encased in a new bone of exactly 

 the same shape, which is perforated by numerous holes, through 

 which the old bone exfoliates. 



Causes. — In man it not unfretjuently arises from constitutional 

 causes, — scrofula, etc. ; but in the lower animals it generally arises 

 from local causes, mechanical injuries, extensive destruction of the 

 surrounding soft parts, especially if it involves the artery supply- 

 ing nourishment to the bone. In young thoroughbred horses, we 

 are familiar with it from sore shins, which ari.ses from the animal 

 being put in training too young. The concussion sets up inflam- 

 mation of the periosteum, which may be followed by caries, but 

 more commonly necrosis of the cannon bone. 



Symptovis.— The external appearances do not difter very 

 materially from caries. We have sinuses penetrating the bone, 

 from which there is a copious dischai-ge of most offensive-smelling 

 matter, in which are occasionally discharged pieces of dead bone 

 which have escaped through tl^s holes in the new bone. This is 

 called the process of exfoliation. It is easily distinguished from 

 caries by the surface of the bone not being worm-eaten, but 

 smooth, and studded with numerous holes. Again, it is not soft, 

 as in caries ; it cannot be punctured with the probe, and it is as 

 heavy, if not heavier, than in health. 



Treatment. — It must be treated on the same principle as 

 caries. The sinuses must be kept open, frequently washed out, 

 and sonic stimulant injected, as hydrochloric acid (diluted), and 

 tonics, and good food must from the first be given. 



48 



