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. 
Fistule 
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 eases 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 
