WOUNDS AND THEIR TREATMENT. '503 
>“ Fistulous tracts are lined with a false, or adventitious, membrane 
and show no disposition to heal. They constantly afford means of 
exit to the pus or ichorous material discharged by the unhealthy 
parts below. They are particularly liable to develop at the withers 
or poll because of the exposed positions which these parts occupy, 
and, having once become located there, they usually assert a tendency 
to further extension, because the vertical and laminated formation 
of the muscles and tendons of these parts allows the forces of gravi- 
tation to assist the pus in gaining the deeper-lying structures and 
also favors its retention among them. 
Causes.—Fistulas follow as a result of abscesses, bruises, wounds, 
or long-continued irritation by the harness. Among the more com- 
mon causes of fistula of the poll (poll evil) are chafing by the halter 
or heavy bridle; blows from the butt end of the whip; the horse 
striking his head against the hayrack, beams of the ceiling, low doors, 
etc. Fistulous withers are seen mostly in those horses that have thick 
necks as well as those that are very high in the withers; or, among 
saddle horses, those that are very low in the withers, the saddle here 
riding forward and bruising the parts. In either of these locations 
ulcers of the skin, or simple abscesses, if not properly and punctually 
treated, may become fistulas. They are often caused by bad-fitting 
collars or saddles, by direct injuries from blows, and from the horse 
rolling upon rough or sharp stones. The pus burrows and finds lodg- 
ment deep down between the muscles, and escapes only when the sinus 
becomes surcharged or when, during motion of the parts, the matter 
is forced to the surface. 
Symptoms.—These, of course, will vary according to the progress 
made by the fistula. Following an injury we may often notice sore- 
ness or stiffness of the front legs, and upon careful examination of 
the withers we see small tortuous lines running from the point of 
irritation downward and backward over the region of the shoulder. 
These are superficial lympthatics, and are swollen and painful to the 
touch. In a day or two a swelling is noticed on one or both sides of 
the dorsal vertebrae, which is hot, painful, and rapidly enlarging. 
The stiffness of the limbs may disappear at this time, and the heat 
and soreness of the parts may become less noticeable, but the swelling 
remains and continues to enlarge. 
A fistulous ulcer of the poll may be first indicated by the opposition 
which the animal offers to the application of stable brush or bridle. 
At this time the parts are so sore and sensitive that there is some 
danger that unless handled with the greatest care the patient will 
acquire disagreeable stable habits. The disease in its early stages 
may be recognized as a soft, fluctuating tumor surrounded by inflam- 
matory swelling, with the presence of enlarged lymphatic vessels and 
stiffness of the neck. Later the inflammation of the surrounding tis- 
