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 thei 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- 



