168 The Diseases of Animals 



oil." If the abscess is in the vicinity of large blood- 

 vessels or important organs, suitable precautions should 

 be taken to prevent injury to them. 



Fistulce 



A fistula is a running sore that sometimes results 

 from a wound or abscess, and does not heal readily, but 

 persists in discharging pus, often for long periods. 

 Sometimes a foreign body in the tissues is the cause 

 of the fistula, or a piece of denuded bone or diseased 

 cartilage. In other cases the fistula is a tube or 

 series of tubes, or a cavity lined with a smooth 

 " false membrane " which must be destroyed before 

 the part will heal. 



Poll -evil 



This disease, which partakes of the nature of a cold 

 abscess as well as a fistula, occurs in horses on the top 

 of the head or on the neck close to the head. A poll- 

 evil is generally believed to be brought on by an injury, 

 such as hitting the head against the ceiling, pulling 

 on the halter, or by overcheck. In many cases it is 

 difficult to assign the cause, but the disease is prob- 

 ably caused by bacteria invading the tissues of 

 that region. 



The first symptom of poll -evil is a rather firm, puffy 

 swelling that occurs on the top, or on one or both 

 sides of the top of the neck. There is usually little 

 pain in the early stages, but later the increased pres- 

 sure of the pus causes the horse some pain and he 



